Calculator Comparison

Features in optional ROMs are listed as Option. Features in HP mag card or tape Application Pacs are listed as +. Other software is not included.
Display and Keyboard	HP-65	HP-55	HP-25
Display type	LED	LED	LED
Display format	1 Line	1 Line	1 Line
FIXed number format	Yes	Yes	Yes
SCIentific number format	Yes	Yes	Yes
ENGineering number format	-	-	Yes
STanDard / ALL number format	-	-	-
Alpha messages and prompts	-	-	-
Softkeys labeled by mag. card or overlay	Yes	-	-
Softkeys labeled by display menus	-	-	-
Softkeys with neither labeling system	-	-	-
Status annunciators	-	-	-
Redefinable keyboard	-	-	-
Logic	HP-65	HP-55	HP-25
Logic system	RPN	RPN	RPN
Stack levels	4	4	4
Last x	Yes	Yes	Yes
Undo	-	-	-
Precedence	-	-	-
Parentheses	-	-	-
Storage Addition (STO +)	Yes	-	Yes
Storage Arithmetic (STO +, −, ×, ÷)	Yes	-	Yes
Storage Exponentiation (STO ^)	-	-	-
Recall Arithmetic	-	-	-
Named variables	-	-	-
Multiple data types	-	-	-
Directories	-	-	-
Math	HP-65	HP-55	HP-25
+, −, ×, ÷	Yes	Yes	Yes
1/x	Yes	Yes	Yes
√	Yes	Yes	Yes
x²	Yes	Yes	Yes
LOG x	Yes	Yes	Yes
10^x	Yes	Yes	Yes
LN x	Yes	Yes	Yes
e^x	Yes	Yes	Yes
y^x	Yes	Yes	Yes
π	Yes	Yes	Yes
%	-	Yes	Yes
% change	-	-	-
INTeger truncation and ABSolute value	Yes	-	Yes
Trigonometric functions (SIN, COS etc.)	Yes	Yes	Yes
Hyperbolic trig. (SINH, COSH etc.)	+	-	-
# of trig. modes (degrees, radians, grads)	3	3	3
Advanced Math	HP-65	HP-55	HP-25
Solver / root finder	+	-	-
Numeric integration	+	-	-
Complex numbers	+	-	-
Matrix operations	+ (2×2)	-	-
Matrix writer	-	-	-
Equation writer	-	-	-
Symbolic operations	-	-	-
Fractions	-	-	-
Plotting and graphics (display)	-	-	-
Plotting and graphics (printer / plotter)	-	-	-
Statistical	HP-65	HP-55	HP-25
Mean, standard deviation (# of variables)	+	2	1
Σ of n, x, x²	+	Yes	Yes
Σ of n, x, x², y	+	Yes	Yes
Σ of n, x, x², y, xy	+	Yes	Yes
Σ of n, x, x², y, y², xy	+	Yes	-
Σ of lists	-	-	-
Random number generator	+	-	-
Linear regression, estimate	+	Yes	-
Curve fitting	+	-	-
Correlation coefficient	+	-	-
Normal distribution	+	-	-
Factorial	Yes	Yes	-
Gamma	-	-	-
Combinations and permutations	+	-	-
Scientific and Time	HP-65	HP-55	HP-25
Polar / rectangular conversions	Yes	Yes	Yes
Base conversions (2, 8, 10, 16)	Octal, +	-	-
Arithmetic in bases 2, 8 and 16	+ (octal)	-	-
Bit operations (AND, OR, XOR, ...)	-	-	-
Selectable word size (1-64 bits)	-	-	-
Selectable complement mode (1's, 2's, unsigned)	-	-	-
Decimal hrs / hrs.min.sec. conversions	Yes	Yes	Yes
Hrs.min.sec arithmetic	Yes	Yes	-
Time of day clock	-	-	-
Timer	-	Yes	-
Dynamic calculations (timer × rate)	-	-	-
Alarms	-	-	-
Unit Conversions	HP-65	HP-55	HP-25
Centimeters / inches	some	-	-
Millimeters / inches	-	Yes	-
Meters / feet	-	Yes	-
Kilograms / pounds (mass)	-	Yes	-
Newtons / pounds (force)	-	Yes	-
British thermal units / joules	-	Yes	-
Liters / gallons	-	Yes	-
° Celsius / ° Fahrenheit	-	Yes	-
Other	-	-	-
User-defined units	-	-	-
Time Value of Money	HP-65	HP-55	HP-25
Number of payments (n)	+	-	-
Interest rate (i)	+	-	-
Present Value (PV)	+	-	-
Payment (PMT)	+	-	-
Future Value (FV)	+	-	-
Cash Flow Analysis	HP-65	HP-55	HP-25
Net present value (NPV)	+	-	-
Internal rate of return (IRR)	+	-	-
Amortization	HP-65	HP-55	HP-25
Accumulated Interest (ACC INT)	+	-	-
Balance (BAL)	+	-	-
Depreciation	HP-65	HP-55	HP-25
Straight line (SL)	+	-	-
Sum of the years digits (SOYD)	+	-	-
Declining balance (DB)	+	-	-
Bonds and calendar functions	HP-65	HP-55	HP-25
Bond price	+	-	-
Bond yield	+	-	-
Date arithmetic / calendar functions	+	-	-
Memory and Programming	HP-65	HP-55	HP-25
Programming language(s)	RPN	RPN	RPN
RAM / Max # of variables or addressable registers	9 Registers	20 Registers	8 Registers
Max # of program steps	100	50	49
RAM / Max vars or regs with full optional RAM	-	-	-
Max # of prog steps with full optional RAM	-	-	-
Merged program steps	Partially	-	Yes
Manual register / program memory allocation	-	-	-
Automatic register / program memory allocation	-	-	-
Overlapped register and program memory	-	-	-
Continuous memory	-	-	-
Flags	2	-	-
Conditional tests	4	2	8
Subroutine levels	1	-	-
Indexed looping (increment by +/- 1, end at 0)	Yes	-	-
Indexed looping (choice of increment and end)	-	-	-
Multiple index / loop registers	-	-	-
Line number addressing	-	-	Yes
Branching by relative line number	-	-	-
Global program label addressing	Yes	-	-
Local program label addressing	-	-	-
Indirect / computed addressing and control	-	-	-
Multiple indirection registers	-	-	-
Pause	-	-	Yes
Alpha messages and prompts in programs	-	-	-
Alpha program listings	-	-	-
Alpha string manipulation	-	-	-
Program step insert / delete	Yes	-	-
I/O and Expansion Features	HP-65	HP-55	HP-25
ROM modules	-	-	-
RAM modules or expansion option	-	-	-
General expansion slots / connector	-	-	-
Magnetic card reader/writer	Yes	-	-
Tape drive	-	-	-
Disk drive	-	-	-
Upgradeable firmware	-	-	-
Optical wand	-	-	-
Serial port	-	-	-
Infrared input	-	-	-
Infrared output	-	-	-
Printer	-	-	-
Networking	-	-	-
Other	-	-	-
General	HP-65	HP-55	HP-25
Sounds	-	-	-
Self test	-	-	-
Hard case (in addition to soft case)	Yes	Yes	-
Additional Features	-	-	-
Batteries	Rechargeable	Rechargeable	Rechargeable
Length (inches)	6.0"	5.8"	5.1"
Width	3.2"	3.2"	2.7"
Height	1.4"	1.3"	1.2"
Weight (oz or lbs)	11 oz	8.7 oz	6 oz
Year of introduction	1974	1975	1975
Features in optional ROMs are listed as Option. Features in HP mag card or tape Application Pacs are listed as +. Other software is not included. Unlim means limited only by available memory.

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Display and Keyboard

HP-65

HP-55

HP-25

Display type

LED

Display format

1 Line

FIXed number format

Yes

SCIentific number format

Yes

ENGineering number format

Yes

STanDard / ALL number format

Alpha messages and prompts

Softkeys labeled by mag. card or overlay

Yes

Softkeys labeled by display menus

Softkeys with neither labeling system

Status annunciators

Redefinable keyboard

Logic

HP-65

HP-55

HP-25

Logic system

RPN

Stack levels

Last x

Yes

Undo

Precedence

Parentheses

Storage Addition (STO +)

Yes

Storage Arithmetic (STO +, −, ×, ÷)

Yes

Storage Exponentiation (STO ^)

Recall Arithmetic

Named variables

Multiple data types

Directories

Math

HP-65

HP-55

HP-25

+, −, ×, ÷

Yes

1/x

Yes

√

Yes

x²

Yes

LOG x

Yes

10^x

Yes

LN x

Yes

e^x

Yes

y^x

Yes

Yes

% change

INTeger truncation and ABSolute value

Yes

Trigonometric functions (SIN, COS etc.)

Yes

Hyperbolic trig. (SINH, COSH etc.)

# of trig. modes (degrees, radians, grads)

Advanced Math

HP-65

HP-55

HP-25

Solver / root finder

Numeric integration

Complex numbers

Matrix operations

+ (2×2)

Matrix writer

Equation writer

Symbolic operations

Fractions

Plotting and graphics (display)

Plotting and graphics (printer / plotter)

Statistical

HP-65

HP-55

HP-25

Mean, standard deviation (# of variables)

Σ of n, x, x²

Yes

Σ of n, x, x², y

Yes

Σ of n, x, x², y, xy

Yes

Σ of n, x, x², y, y², xy

Yes

Σ of lists

Random number generator

Linear regression, estimate

Yes

Curve fitting

Correlation coefficient

Normal distribution

Factorial

Yes

Gamma

Combinations and permutations

Scientific and Time

HP-65

HP-55

HP-25

Polar / rectangular conversions

Yes

Base conversions (2, 8, 10, 16)

Octal, +

Arithmetic in bases 2, 8 and 16

+ (octal)

Bit operations (AND, OR, XOR, ...)

Selectable word size (1-64 bits)

Selectable complement mode (1's, 2's, unsigned)

Decimal hrs / hrs.min.sec. conversions

Yes

Hrs.min.sec arithmetic

Yes

Time of day clock

Timer

Yes

Dynamic calculations (timer × rate)

Alarms

Unit Conversions

HP-65

HP-55

HP-25

Centimeters / inches

some

Millimeters / inches

Yes

Meters / feet

Yes

Kilograms / pounds (mass)

Yes

Newtons / pounds (force)

Yes

British thermal units / joules

Yes

Liters / gallons

Yes

° Celsius / ° Fahrenheit

Yes

Other

User-defined units

Time Value of Money

HP-65

HP-55

HP-25

Number of payments (n)

Interest rate (i)

Present Value (PV)

Payment (PMT)

Future Value (FV)

Cash Flow Analysis

HP-65

HP-55

HP-25

Net present value (NPV)

Internal rate of return (IRR)

Amortization

HP-65

HP-55

HP-25

Accumulated Interest (ACC INT)

Balance (BAL)

Depreciation

HP-65

HP-55

HP-25

Straight line (SL)

Sum of the years digits (SOYD)

Declining balance (DB)

Bonds and calendar functions

HP-65

HP-55

HP-25

Bond price

Bond yield

Date arithmetic / calendar functions

Memory and Programming

HP-65

HP-55

HP-25

Programming language(s)

RPN

RAM / Max # of variables or addressable registers

9 Registers

20 Registers

8 Registers

Max # of program steps

100

RAM / Max vars or regs with full optional RAM

Max # of prog steps with full optional RAM

Merged program steps

Partially

Yes

Manual register / program memory allocation

Automatic register / program memory allocation

Overlapped register and program memory

Continuous memory

Flags

Conditional tests

Subroutine levels

Indexed looping (increment by +/- 1, end at 0)

Yes

Indexed looping (choice of increment and end)

Multiple index / loop registers

Line number addressing

Yes

Branching by relative line number

Global program label addressing

Yes

Local program label addressing

Indirect / computed addressing and control

Multiple indirection registers

Pause

Yes

Alpha messages and prompts in programs

Alpha program listings

Alpha string manipulation

Program step insert / delete

Yes

I/O and Expansion Features

HP-65

HP-55

HP-25

ROM modules

RAM modules or expansion option

General expansion slots / connector

Magnetic card reader/writer

Yes

Tape drive

Disk drive

Upgradeable firmware

Optical wand

Serial port

Infrared input

Infrared output

Printer

Networking

Other

General

HP-65

HP-55

HP-25

Sounds

Self test

Hard case (in addition to soft case)

Yes

Additional Features

Batteries

Rechargeable

Length (inches)

6.0"

5.8"

5.1"

Width

3.2"

2.7"

Height

1.4"

1.3"

1.2"

Weight (oz or lbs)

11 oz

8.7 oz

6 oz

Year of introduction

1974

1975

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Unlim means limited only by available memory.

HP-65 notes:

The HP-65 had an unusual f^-1 key, which invoked the inverse of the printed function.
FIX mode was set by pressing DSP . # (# was the number of desired digits)
SCI mode was set by pressing DSP #
The only looping function was DSZ, which decremented register R8 until it reached 0.
Register R9 was overwritten by trig functions, polar rectangular conversions. During conditional tests, R9 served as a Last x register.
The HP-65 powered up with programs entered to give default functions to the A-E keys (1/x etc.). They provided unshifted access to these functions when other programs weren't in use.
When a subroutine was called, the 65 kept track of the return address by inserting a marker instruction into the program memory. If you stopped a program while in a subroutine, you could switch to program mode, move to the return address and actually see the marker. (Which displayed as a 41 keycode - same as Enter.)
Medical pac has some conversions.

HP-55 notes:

20 registers are 0 - 9 and .0 - .9. Had separate functions (CLR and CL.R) for clearing 0-9 and .0-.9. This was handy because timer splits were stored in registers 0-9.

HP-25 notes:

The HP-25C has a separate features page.

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