The Museum of HP Calculators

Collector's Corner

This page provides information primarily of interest to HP calculator collectors.

Topics are:
Difficulty Of Obtaining Various Models (And Prices)
Series Names
Code Names
Variations, Special Models and Bugs
Battery Packs & Chargers
Decoding Serial Numbers
Earliest Serial Numbers (so far)
Self Tests
How To Build A Limited Collection
Where To Find Them
How To Buy Them (Remotely)
Where To Get Supplies

Difficulty Of Obtaining Various Models (And Prices)

The following guide groups calculators into broad categories based on the difficulty of obtaining. (This is mostly a matter of how hard they are to find, but more difficult models tend to cost more especially if purchased from a collector or dealer.) The difficulty ratings are for working models in extra fine to new condition. These are all relative ratings. Even an "easy" model requires some effort.

By popular demand, price ranges recently observed have been added. Take these prices with a grain of salt however as some of them are based on a single sample and all of them are based on less than ten. These prices are for public sales between collectors typically advertised on the Internet. All prices are for calculators described as being in at least "very good" condition and working.

Please note that if a price isn't listed here, then I don't know it. I don't try to track prices of slide rules and other brands of calculators.

These price ranges do not include the bargains you can find in flea markets, government and business liquidation sales or by trolling regional for sale groups. Cheap HPs can be found if you're willing to spend the time. Generally, calculators at the high end of the price ranges were sold via "best offer" advertisements on the net or in online auctions such as eBay.

2001 Update: Prices on eBay continue to escalate while Cheap HPs can still be found (but it is getting more difficult.) Two recent debates over eBay pricing on the HP forum have involved large eBay dealers posting under aliases. The (aliased) dealers claimed that the eBay prices are the only "real" prices because that's what people will pay.

The US stock crash of 1929 is attributed to people paying "the going price" for the stocks of good companies without regard to fundamental value. 1999 was similar but the US stock market has been much more resilient (at least so far.) While the most absurdly priced issues dropped in 2000, the price of the market overall as of mid-2001 is still very high based on historical fundamentals.

Of course, placing a fundamental value on an old calculator is much harder. Have on-line auctions lead to a "new era" of HP calculator collecting or is this just the latest collectable to go through a speculative bubble? If the latter, will the landing be hard or soft? Only time will tell.

Price range decoder:

Model Difficulty Price Range
(see above)
HP-01 (1) Extra Difficult! $350, $1100, $1325, $2000, $3044
HP-01 (incomplete) Very Difficult $625, $760, $1848
HP-10 Very Difficult $250, $305, $400
HP-10C (2) Very Difficult $80, $102-$261, $400
HP-11C Easy $46, $77, 90-$117, $152, $157, $212
HP-14B Easy  
HP-15C Moderate $50, $96-$199, $247, $306(6) $323(6), $329, 455(6)
HP-16C Moderate $25(8), $30, $71-$260, $280, $300, $301, $480(6), $842(8)
HP-17B Easy $26-$38
HP-18C Moderate $20, $50, $60
HP-19B Easy  
HP-19C Difficult $100-$410
HP-21 Easy $16-$110
HP-21S Easy  
HP-22 A Bit Difficult $50-$162
HP-22S Fairly Easy $50, $75, $125
HP-25 Easy $35-$140, $202
HP-25C Moderate $75
HP-27 Difficult $70-$90, $270, $355
HP-27S Moderate $32, $86, $101, $150
HP-28C Easy $35-$50, $128
HP-28S Easy $45-$66, $114
HP-29C Moderate $143-$232, $365, $475
HP-31E (2) Difficult $50-$128
HP-32E Easy $25-$45, $113, $155
HP-32S Easy $30, $40, $75-$115
HP-33E Easy $30-$68, $91
HP-33C Fairly Easy $50-$186
HP-34C Easy $46-$150, $177, $202, $205
HP-35 (most types) Fairly Easy $71-$186
HP-35 (all legends on keys) Moderate $100
HP-35 (red dot) (7) Very Difficult $300, $597, $600, $601, $756
HP-37E Easy $40, $60
HP-38C Moderate $117
HP-38E Easy $41, $99
HP-41C (3) Easy $40-$90
HP-41C (option 001/blank) A Bit Difficult $101-112, $200
HP-41CV (3) Easy $65-$91, $125, $135
HP-41CX (3) Fairly Easy $85-$127, $180, $200, $230, $280
HP-42S (3) Fairly Easy $95-$202, $260, $400
HP-45 Fairly Easy $50, 63-$123, $180, $346(6)
HP-46 Very Difficult $100, $143, $167, $197-$250, $450
HP-48S Easy $35, $57
HP-48SX Easy $50-$80
HP-55 A Bit Difficult $12, $75-$110, $127, $203, $228
HP-65 Difficult $96-$352, $450, $845, $1,045
HP-67 Easy $65, $92-$225, $315, $352, $450
HP-70 Very Difficult $285, $447
HP-71B Easy $35-$110
HP-75C (5) Fairly Easy $3-$50, $100
HP-75D (5) Fairly Easy $3-$35, $130
HP-80 A Bit Difficult $25, $97-$160, $204, $238, $385
HP-81 Very Difficult $225
HP-83 Moderate $90
HP-85 Fairly Easy $53, $100
HP-86 Fairly Easy  
HP-87 Moderate $60
HP-91 A Bit Difficult $200, $289
HP-92 Difficult $275
HP-94 (4) Extra Difficult $105, $250, $300, $325, $350, $370
HP-95C Most Difficult  
HP-97 Fairly Easy $76-$202, $227
HP-97S Very Difficult $200, $275, $300
HP-9100 Very Difficult $750, $800, $1225, $1700
HP-9805 Extra Difficult $150, $360, $413
HP-9810 Difficult $184,  $500
HP-9815 A Bit Difficult  $100, $150, $256
HP-9820 Difficult  $200, $300
HP-9825 Moderate  $30, $67, $150
HP-9830 Difficult  $100, $270, $280

(1) The HP-01 is not really as rare as most other Extremely Difficult and even some Very Difficult models but everyone knows it's a great collectible so it's very hard to obtain. The "incomplete" entry refers to a sample missing, any of the following: pen stylus, clasp stylus. (Several less-than-excellent samples have sold recently in the $300-$800 range.)

(2) Some low-end models like the HP-10C and HP-31E are hard to find as they tend to get thrown away. The good news that you can sometimes get them for throw-away prices. The $400 HP-10C was described by the seller as "new in the box".

(3) HP-41s were very popular and therefore very common. However, their popularity persists among some users so don't be surprised if some owners refuse to sell at any price. The recently discontinued HP-42S also has fans that will pay very high prices. Some HP-41C accessory prices that have been seen on eBay:

(4) If you really want to impress your collecting friends, collect one each of the HP-94D, HP-94E, and HP-94F.

(5) Around 2000, HP-75C and D prices were depressed by recent large-scale sales by several companies and government agencies. (The $3 price required the purchase of at least 25 units. Quantity 1 pricing usually starts at $20.)  The high-priced samples were described as "new in the box".

(6) Described as Mint In Box and complete.

(7) The red dot shows through a hole to the right of the power switch. The dot does not light up.

(8) The $842 price (ebay) and the $25 price (offline sale) for an HP-16C were reported to the museum in the same week in 2002.

Difficulty ratings are based on the experiences of the curator and a few other collectors. Your mileage may vary.

Series Names

Many beginning collectors are confused by series names that are often used when discussing HP calculators. These names are HP's own code-names for the product lines (though the history of the "classic" name is unsure.)

The first series of calculators (HP-35, HP-45, HP-55, HP-65, HP-70 and HP-80.) The HP-67 is also regarded as a classic even though it is based on Woodstock series technology. This name was probably given well after the fact. (HP wasn't sure at the time whether there was really a market for the HP-35.)
Classic Printers
The HP-46 and HP-81.
The second major series (The HP-21 through HP-29). Apparently named after the small yellow character in the Peanuts cartoons.
The 90 series (HP-91, HP-92, HP-95C, HP-97 and HP-97S). Definitely top of the line.
The 30E/C series (HP-31E through HP-38C).
The HP-10 and HP-19C. (Don't confuse these with the voyager series.)
HP-41C, HP-41CV and HP-41CX.
Later HP-41 series models with reduced electronics.
The 10C series (ie HP-10C, HP-11C through HP-16C). (Do not confuse the HP-10C with the HP-10B or the HP-10.)
The calculators that fold. Also called the Clamshell series.
The current lower end series including most models ending in B (business), S (scientific) and II.
A series that never went into production. The only known model is Earthquake - a follow-on to the HP-65.
A series that never went into production. No details known.

Code Names

Many HP calculators had internal code names during their development. The following code names are known:






















HP-33C—Sage C




HP-38C—Chive C













HP-49G—Copernicus or V'ger
















Some code names that didn't make it to production:

Earthquake (quake)
Follow-on to the HP-65. Originally planned as an interim product between the HP-65 and Roadrunner (below.) The schedule on this slipped and the product became much too close to Roadrunner. Notes at an HP meeting suggest a major redefinition looking at combining the platform for Roadrunner and EarthQuake involving the use of peripherals such as a printer or plotter. Of course, Roadrunner also never appeared but the concept of the HP-65 follow-on sharing a platform with a higher end model (eventually Kittyhawk) minus a printer was kept in the HP-67/97. A concern was also expressed that Roadrunner, Kittyhawk and Earthquake all had their own programming languages. This was also fixed in the 67/97.
Phoenix / Squish II
Reduced cost Woodstock member. A 6 chip N-channel and CMOS scientific meant as a sequel to the HP-55.
Business desktop with printer capable of "calculating, tabulating and clock functions".
Thunderbolt I / Thunderbolt II (HP-21B)
A 21 sequel meant to sell for around $85. The Thunderbolt I was intended to be a rechargeable unit with an AC adaptor and the Thunderbolt II was meant to run on disposable batteries. The name HP-21B was later assigned.
High performance programmable with bubble memory and an LCD display. It would have been HP's first LCD if it had gone into production. It probably would have been an HP-9x model. It would seem that the physical design was meant to be just like the Topcats because a concern was expressed about how to hide the card reader behind a clear display.
Small fourth generation handheld featuring all CMOS technology. Meant as a Phoenix replacement (which also never shipped.) Disposable batteries, clock functions and "elegant packaging".
Kittyhawk was eventually released as the HP-97, but at one point it was probably the code name for the HP-66. It included a tape drive, speaker and "gobs of features" according to the minutes of a 1975 product planning meeting. At the time of the meeting is was not related to or software compatible with the HP-67.
From the minutes of a product planning meeting: "A suggestion was made to put all of Cricket's technology into an elegant, truly pocket-size calculator selling for around $250. It would have an LED readout, 10 keys, 2 ROMS, timing functions and do about '40 things'. The appearance of the package would do justice to the selling price. This suggestion prompted an immediate lack of enthusiam [sic] and was seconded by no one thus inhibiting further serious discussion." This was a suggestion to "save" Cricket (HP-01) which was highly controversial. The meeting recap/action item related to Cricket was: "Pray for Cricket."

Variations, Special Models and Bugs

Some HP calculators had manufacturing variations. This page lists relatively obvious changes. Some details like the exact plastic and trim colors, and minor ROM revisions are not listed. This page also doesn't list the many singular oddities that collectors have found such as HP-25s that have continuous memory etc. Most of these are probably the result of swaps during repairs.

Comma and Dot Variations

Some HP calculators made for the European market had the commas and dots reversed as compared to their American counterparts. The 20 series used two different displays with the decimals being either square or triangular. The triangular decimals could be interpreted as either dots or commas and so were sold in both the US and Europe. The 30 series models had a jumper change between European and U.S. comma/point formats. (Many later models can be switched by the user.)

Serial Number Placement

Serial numbers on classic models were printed on stickers applied between the feet or in the battery compartment. 20 series (and HP-10 and 19C) serial numbers were molded/heat stamped into the plastic on the bottom or printed on stickers in the battery compartment. 10C series serial numbers were placed in the same general area but their exact position varies noticeably.

Anniversary Models

There have been a number of calculators made to celebrate certain anniversaries. The HP-14B and HP-32S were made with gold anniversary logos to celebrate HP's 50th anniversary. Some recent anniversary models are shown in the photo gallery.

Classic Power Labels

The power/patent labels on most Classic calculators are in mostly uppercase with the power consumption stated as 500mW (500 milliwatts). Some are completely uppercase with the power consumption stated as 500MW. Technically that's 500 megawatts but many power consumption labels are 100% caps so this is generally understood to still mean milliwatts.

HP 9810 Versions

Early 9810s had a single LED for unit for each digit. Later models used the same five-digit LED elements found in the classic calculators.

HP-35 Versions and Bugs

The HP-35 underwent many major physical revisions as shown in the HP-35 exhibit.

  1. Only the first version had a red dot that showed when the calculator was on. It also had a raised spot on the "5" key. The serial number was on the back between the rubber feet. The serial number on these starts with 1143A.
  2. The second version looked like the first but omitted the red dot. Early samples of this version still had a raised spot on the "5" key. The serial number was moved inside the battery compartment. Some of these also have serial numbers starting with 1143A.
  3. The first two versions were simply labeled "Hewlett Packard" without a model number while this and the next version was labeled "Hewlett Packard 35".
  4. In the last version, the upper rows of keys became black and rectangular rather than blue and square and the labels were molded into the keys rather than printed above them. This last version also had molded rather than painted "On" and "Off" legends and had just one silver trim bar below the display whereas versions 1-3 had 2.

The early HP-35s had a major ROM bug that caused: 2.02 ln ex to display a result of 2. There was also a bug in the trigonometric functions for certain inputs. Some examples were:

Function      Buggy      Correct
ARC SIN 0.0002 5.729577893 x 10E-3 0.01145916
ARC COS 0.0002 89.99427042 89.98854
ARC TAN 0.0002 5.729577893 x 10E-3 0.01145916
ARC TAN 1.00020002 45 45.00573

These bugs were quickly fixed and HP recalled early units for an upgrade.

HP-80 Versions

Like the HP-35, early HP-80s were labeled "Hewlett Packard" with no model number. "80" was added to later models. On early versions, the trim strip above the power switch was a piece of metal. Later versions went back to the vacuum-deposited trim used in other classic models. Like the HP-35 and HP-45, early versions had "On" and "Off" painted in white and later versions were molded.

HP-45 Versions

The HP-45 can be found with "On" and "Off" molded or painted on. Like the HP-80, early versions had a metal strip above the power switch to avoid wear on the silver trim.

On later HP-45s the direction of STO - r and STO ÷ r was reversed. The manuals were also updated but some of the earliest model to be shipped with the later semantic came with a separate update page for the early manual.

STO - r r = x - r r = r - x
STO ÷ r r = x ÷ r r = r ÷ x

HP-9825A Versions

HP-9825As can be found with either low profile snap keys or more conventional taller keys.

HP-25 Versions

Some HP-25s have several bugs including polar/rectangular conversion errors for angles within +/- 0.000573° of 180° . Also when the last operation caused data in a certain range to be stored in a register and the calculator was at step 00, switching to Program mode would cause a blank display and switching back to Run would display Error.

HP-67/97 Bugs

Earlier HP-67 and HP-97s had bugs affecting SIN-1, COS-1, and TAN-1 functions. For these functions Last X was not saved when X was 0 or -1. A few specific arguments produced errors such as:

Function      Buggy      Correct
SIN-1 0.000003000 1.730332541E-4 1.718873385E-4
SIN-1 0.000004000 2.349126960E-4 2.291831181E-4
SIN-1 0.000005000 2.979380535E-4 2.864788976E-4

(The arguments must be exact to produce the errors.)

HP-01 Versions

HP-01s in both gold and stainless steel can be found with bronze or black-colored buttons as shown in this comparison photo (27K) which shows a 1978 version on the left and a 1977 version on the right. See the HP-01 page for both versions in stainless steel. Earlier bracelets had links whose edges were polished to a mirror finish whereas later versions were brushed. Later versions added the legends "U.S. & Foreign Components" to the case back and "or plaque galvanique 10" to the bracelet clasp. Later gold versions omitted the gold plating from inside the clasp.

HP-10 and HP-19C Versions

These calculators can be found with or without a security cable attachment bracket. The bracket is metal and pivots out from the back right corner.

30 Series Versions

On some versions, the keypad was metallic and had a smooth finish with metallic gold or silver trim. On other versions the keypad was plastic and the trim was light grey or light brown. The texture of the plastic keypads ranged from smooth to textured/matte.

The 30 series also had two very different construction techniques.

HP-41C Versions

Early HP-41Cs used the same key shape used in the 20 and 30 series. Later HP-41Cs had lower keys with a gentler slope for the front (alpha) label. The exact colors, feel of the keyboard, and texture of the keypad vary somewhat over the calculator's long run. Later "Halfnut" versions had redesigned and simplified electronics. All HP-41s can be found in Halfnut versions although CVs and CXs are much more common than Cs.

Early HP-41Cs had gold-plated ball-bearings on the side of the battery compartment to allow for a future AC adaptor that was never produced. When HP introduced the rechargeable battery pack with its own charger connector, the ball bearings were omitted from the calculators

Early HP-41Cs had a number of bugs including not checking STO IND and RCL IND for proper range which allowed accessing system registers. The IND modifier also allowed out-of-range augments for flag operations. Early models also calculated SIN incorrectly for small angles and the CLP function would only clear up to 1089 lines.

The HP-41C Option 001 ("Blanknut") can be found with or without a piece of plastic that covers the USER and PRGM keys. Most are HP-41CVs internally but some are HP-41CXs. Some, but not all, Option 001s have halfnut electronics. Some Option 001 Models don't have serial numbers.

10C Series Versions

Versions can be found with the HP logo/model number in either highly reflective glossy silver or a matte-finished silver. Later models had painted rather than molded key legends.

Late versions of the HP-11C, 15C and 16C were made with HP-12C keys that were either (re)painted or were made using worn molds for other keys. Some HP-16Cs had HP-12C keys that were first repainted to be HP-15C keys and then repainted to be HP-16C keys, or the final mold was used for three different keys. The picture below shows an HP-16C "F" key over an HP-12C "CHS" key. Some HP-12Cs also had keys that were repainted/reused.

This appearance could be the result of repainting or of using the final mold for the CHS key for the final step in double-shot molding the F key. Reusing the mold would create the same appearance since the step of pressing the already-molded symbol into the final mold many times would create wear in the mold (even though it is much harder than plastic). (Re)painting seems to be the dominant theory among collectors (probably due to being first), but the curator believes that reuse of molds is more likely since these keys are clearly double-shot molded and repainting would have required an entirely different process to be applied to already double-shot molded keys. (Painting would also reduce their durability.) However, at this time, no one has been willing to cut one of these keys apart to see how they were created.

On earlier versions the keyboard and keypad were somewhat glossy, but they were mat with somewhat different printing on the later versions. Also, there are several variations on the printing on the back and in the serial number placement.

Early HP-11Cs had a bug in which if you entered a number in the form 0.0xxx, backspaced over all the digits and then pressed ENTER, 1.00 was entered rather than 0.00. HP allowed users of buggy calculators to swap for fixed units.

Early 10C series units had flat metal springs and clear flexible plastic on both sides of the battery compartment. Later units had a much larger coiled spring with the plastic only on left side. The right side had a fixed gold-plated pin.

The HP-12C has undergone numerous small modifications in its long run.

Pioneer Series Versions

Some versions have the display set deep and others are nearly flush with the top of the calculator. The right contact in the battery compartment may be relatively short and folded or longer and formed in an arc. Singapore versions have a mat serial number area - USA versions are glossy.

Battery Packs & Chargers

Classics (HP-35, 45, 55, 65, 67, 80)
Battery HP 82001B, Chargers HP 00035-60008, HP 03502A, HP 82001A/B, HP 82002A/B/C, HP 82010A (120/240 VAC), HP 82022A(240 VAC), HP 82011A (240 VAC)
Woodstocks (HP-21, 22, 25, 25C, 27, 29C)
Battery HP 82019B, Chargers, HP 82024A (120/230VAC) HP 82026A, HP 82041A/B/C, HP 82025A (230VAC)
Sting (HP-10 and HP-19C)
Battery HP 82052A, Charger HP 82059A/B, (HP 82066A/B, 82068B 240 VAC only)
Spice (HP-31E, 32E, 33E, 33C, 34C, 37E, 38E, 38C)
Battery HP 82109A, Chargers HP 82087A/B (HP 82089B, 82090A/B 220-240 VAC only) Do not use A models on continuous memory calculators
Topcat (HP-91, 92, 95C, 97, 97S)
Battery HP 82033A, Chargers HP 82040A, HP 82059A/B/C/D, (HP 82032, 82066B, 82068B 240 VAC only)
Computers HP-75/D
Battery HP 82001B, Chargers HP 82059B/C/D - not A, (82066B, 82068B 240 VAC only)
Computers HP-94D/E/F
Battery HP 82430A, Charger HP 82431A

Get them while you can! Supplies are dwindling. If you must repair a pack, be careful. You can injure yourself or damage your calculator.

There are several companies that can rebuild battery packs for you or you can make your own from scratch.

Warning! Most models can be damaged if run from the charger without good batteries installed. Only the manuals for the HP 35 and 45 models say that it's OK to run without batteries, but many collectors feel that even those should have batteries installed for maximum protection and long life.

Disposable Batteries

Most modern HPs use AAA, N, or LR44/SR44-type batteries. The later can be confusing because battery numbers vary by company. Some LR44/SR-44 equivalents include:

Compatible cells can be found in both alkaline and silver-oxide. The silver-oxides tend to last much longer on the shelf and in the calculator. (For example: LR44, A76 , EPX76 are alkaline but SR44, 357 and G13 are silver-oxide. Check the package to be sure.) Any photo, electronics or jewelry shop should be able to help you.

Decoding Serial Numbers

Numbers are in the format YYWWC##### where

Is the number of years since 1960.
Is the week (roughly) in which the unit was made. YYWW is not always exact and sometimes may have gone weeks or months without changing.
Is the country code: A = America (USA), B = Brazil, G = Germany, J = Japan, S = Singapore, M = Malaysia or Indonesia.
The serial number within the specified week and year. (This is not included in the Earliest Serial Numbers section because all are assumed to start at 0 or 1.)

Example: The museum's HP-94F is serial number 2622J00025 indicating that it is the 25th unit made in Japan in the 22nd week of 1986.

The correspondence of serial numbers to dates is only approximate. In some cases, they may be better indicators of the date of manufacture of the case or label rather than the entire calculator. With some desktop models, it appears that the date code was changed only when there were manufacturing changes. On the other hand, different versions of the HP-35 can be found with the same date code. (The museum has examples of type 3 and 4 with date code 1346 and some of the type 4s have lower sequence numbers than the type 3s!)

An HP employee wrote to say that date codes at HP were originally changed for engineering /design changes only. This system worked well for a test equipment company. However, calculators sold in higher volumes than previous HP products, which caused the serial numbers to run out. Because of this, HP started changing date codes more frequently. Exactly when this change occurred and whether all manufacturing lines used the same procedure is still unknown.

Sometimes prototypes and test models fall into collectors' hands with no serial numbers or serial numbers in another format. On HP 9825Bs, YY appears to be the number of years since 1970.

Since 1996, some serial numbers have been in the form CCYWW##### where

Is the country code: US = USA, SG = Singapore, ID = Indonesia.
Is the last digit of the year in which the calculator was made. (i.e. a calculator made in 1998 would be marked 8.)
Is the week (give or take) in which the unit was made. These are not always exact.
The serial number within the specified week and year. (This is not included in the Earliest Serial Numbers section because all are assumed to start at 0 or 1.)

Earliest Serial Numbers (so far)

These are the earliest date codes recorded so far for the various models. The date code is the first (left-most) four digits or first 5 characters for some post '96 models. Since this list was based on just a few hundred samples, you may have an earlier date code. If so, please send it to the museum for inclusion here. Please remember that it is the first (left-most) digits that are listed below, not the right-most. The right-most digits are simply a sequence number that is only guaranteed unique for a specific date code. Note that some models make it easy for serial numbers to be swapped so these numbers must be regarded with some suspicion.



































HP-35 T1—1143

HP-35 T2—1143

HP-35 T3—1302

HP-35 T4—1346*


































HP-95C—Pilot #1













* See Variations and Special Models above or the HP-35 exhibit for HP-35 types. One Type 4 with a 1143 code exists but this was probably a serial number swap. Another Type 4 has been found with a date code of 1249 but its back has clearly been removed so it may be another swap.
** This serial number indicates a date more than 18 months before the official CV introduction so it may be a repaired calculator using a back from an HP-41C. ~2040 would be a more conservative estimate for an all-original CV. Earliest Halfnut version found: 2511.
*** The earliest HP-94D recorded starts with 9990 but that's a prototype code.
*4 HP-9825B's used a different numbering system.
*5 Also marked "PROTO". (3321 is the lowest seen non "PROTO" date code.)
*6 For many years, our lowest 48SX was 3001, but then one turned up with 2948. However it has some oddities: case has been opened (or maybe never even closed), and the ROM is in a DIP package with a hand-written label. This could be a development unit.

Self Tests

For Self Test Information, browse to the calculator of your choice and then go to its features page and look in the "notes" section. (The features page is linked near the bottom of each main calculator page.)

How To Build A Limited Collection

Many collectors want advice on how to build a collection that is interesting/proper/important without simply buying every model ever made. Each person must really make their own choice on what to collect but here are a few ideas for your consideration:

One of Each Series

This is for the collector more interested in the packaging and underlying technology of calculators than the exact function set. You would start with the HP 9100 with its core memory, CRT, discrete circuitry and true tank-like construction, followed by one of the HP 9810/20/30 (chips & LEDs), followed by one of the 35/45/65/55/70/80/67, one of the 20 series, one of the 90 series etc...

All The "Early" Models

Simply start from the beginning and work forward to the point of your choice. Many collectors find the earlier models more interesting because some later models are repackaging of earlier functionality. Some collectors avoid LCD models since they are newer and (in theory) have a more limited life.

Desktops Only Or Handhelds Only

Some collect only the desktops because they're the "real machines"/"Big Iron"/etc., because so many features appeared there first or because it's a thrill to own a collection of machines that cost thousands of dollars each when they were new. On the other hand, some collect only handhelds because they're more obtainable, take less room to store or were meant for individuals rather than organizations. There are some crossover products, so to be complete both handheld-only and desktop-only collections should include the HP-46, HP-81 and HP-97S. (The HP-94 is purely a handheld even though its software was developed on another computer.) Note too, that most collectors consider the 90 series to be handhelds even though they're rarely used that way.

The Models That Made History

If you want to collect just the most "significant" models, here are some you should have: HP 9100A (first of all, first programmable, first card reader, first multi-line display, first expandable... etc. etc.), HP 9810 (first chips, first option ROMs, first LEDs and more), HP 9820 (first algebraic - you can skip if you dread "the other system"), HP-35 (first handheld), HP-80 (first business, the beginning of solvers), HP-81 (first use of '.' to address beyond 10 registers), HP-65 (first programmable, first pocket calculator with mass storage, etc.), HP-9825 (first "live keyboard", first true HPL), HP-25C (first continuous memory), HP-27 (business, stat, science in one small package) HP-10 (HP's only adding machine), HP-01 (not just HP's only watch - time and dates as data types), HP-34C (integration/solver), HP-41C (alphanumeric, expansion and I/O now in a handheld), HP-16C (the only one for computer scientists), HP-75C (first portable with BASIC), HP-94 (first backlit LCD, first built-in serial port, first x86 compatible), HP-28C/S (first RPL and first directories on the HP-28S), and HP-48SX expandable RPL, HP-32SII (fractions), HP-95LX (first pocket PC compatible).

Where To Find Them

Prices can vary by factors of more than 100 from the cheap to ultra expensive end of the scales. One dealer claims to make nearly $30,000 per month reselling items on eBay.

Cheap Calculators in 1997

In 1997, the museum picked up extra copies of the relatively rare HP-10C, 31E, 65, 70 and 94D (and several common models) all in excellent or better condition and all for $20 or less. A recent local sale had over a hundred HP-41C modules and options priced at "4 for a dollar". The recently added Friden 132 was picked up for free two weeks after one like it sold for several hundred dollars on eBay. Calculator collecting can still be a low-budget hobby. The trick is to find dealers who haven't seen eBay yet. They're still plentiful but the word is spreading fast so hurry!

Cheap Calculators in 1999

In 1999, one collector reported buying (over a 6 month period) several HP 41's, an HP-38C, 37E, 35, 45, a complete boxed HP-97 and, most recently, an HP-91 with manual. All were purchased at thrift stores for under $10. In 1998, he purchased an HP-70 with manual and multiple accessory books for $2.99. Legwork can still pay off.

In 1999 EduCalc's HP-41, HP-71, and HP-75 stock was being cleared out by Interfab. The items were so reasonably priced that many of them were immediately resold on eBay for 5-20 times as much.

Cheap Calculators in 2001

In 2001 a collector in Switzerland picked up an HP 9100B from a Swiss military institute. The institute had advertised the machine since 1999 and received many emails expressing interest but no one was willing to arrange the transportation. The collector picked it up. The price: Free. This is a technique that the curator has used frequently. Many government agencies and businesses simply won't deal with shipping and there are more within driving range than many people realize. Many of them don't advertise in obvious places. Sometimes the best way to find them is to call the numbers in the phone book and ask.

Cheap and not Cheap Calculators in 2002

During the same week of 2002 an offline sale of an HP-16C was reported at $25, and an Ebay auction finished at $842. (The latter included the box.)  Another collector found an HP-67 and an HP-97 for one dollar at a local surplus store. Both had gummy card reader wheels, but were in great shape otherwise.

Another collector reported: "2nd hand/thrift stores work much better than eBay ... I picked up a 11C (in crumbling case, with only a few scratches) for $1.50 about a month ago, and yesterday, I snagged a 16C (mint in case) for $3."

Cheap Calculators in 2003

In 2003 a European collector reported off-line purchases of a near perfect and nearly complete HP-67 for $65 and a similar condition HP-25 for $50.

Cheap Calculators in 2004

In 2004 a European collector reported off-line purchase of a perfect HP-42S with all accessories for $50.

Cheap Calculators in 2005

In 2005 a collector in Idaho found a working HP-35 (with early bugs) in excellent condition at a local thrift store. It had no scratches or engraving and was priced at $1.50.

Cheap Calculators in 2006

In 2006 a user in Florida found a working HP-11C at a relative's garage sale for 5 cents.

Cheap Calculators in 2007

In 2007 a collector in North Carolina found a working HP-41CX, with box, manuals, and a Stock Forecasting module at a Habitat for Humanity junk store for $1.

How To Buy Them (Remotely)

It's easiest to buy a calculator locally where you can check it over first. If you are buying at a distance, here are some guidelines.

Yes, that's a lot of questions but in any collectibles field, its the more advanced collectors who ask the most questions and end up with the best samples. Of course, you'll rarely get positive answers to all the questions above.

Where To Get Supplies

For older manuals or copies, try the above or try HP on the web or at: (800) 227-8164.

In addition, HP has graciously permitted the museum to make and sell scans of old manuals.

Rechargeable battery packs are becoming difficult to find. There are several companies that can rebuild battery packs for you or you can make your own from scratch.

For thermal paper, try the PM Company. On their website, enter a calculator like HP-97 and Search by Machine.

For other items, please read or post a message in the Museum Classified Ads or in comp.sys.handhelds.

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