The Museum of HP Calculators

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 HP-29C HP-45
Display type LED LED LED LED LED
Display format 1 Line 1 Line 1 Line 1 Line 1 Line
FIXed number format Yes Yes Yes Yes Yes
SCIentific number format Yes Yes Yes Yes Yes
ENGineering number format - - Yes 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 HP-29C HP-45
Logic system RPN RPN RPN RPN RPN
Stack levels 4 4 4 4 4
Last x Yes Yes Yes Yes Yes
Undo - - - - -
Precedence - - - - -
Parentheses - - - - -
Storage Addition (STO +) Yes - Yes Yes Yes
Storage Arithmetic (STO +, −, ×, ÷) Yes - Yes Yes Yes
Storage Exponentiation (STO ^) - - - - -
Recall Arithmetic - - - - Yes
Named variables - - - - -
Multiple data types - - - - -
Directories - - - - -
Math HP-65 HP-55 HP-25 HP-29C HP-45
+, −, ×, ÷ Yes  Yes  Yes  Yes  Yes 
1/x Yes Yes Yes Yes Yes
√ Yes Yes Yes Yes Yes
x2 Yes Yes Yes Yes Yes
LOG x Yes Yes Yes Yes Yes
10x Yes Yes Yes Yes Yes
LN x Yes Yes Yes Yes Yes
ex Yes Yes Yes Yes Yes
yx Yes Yes Yes Yes Yes
π Yes Yes Yes Yes Yes
% - Yes Yes Yes Yes
% change - - - - Yes
INTeger truncation and ABSolute value Yes - Yes Yes -
Trigonometric functions (SIN, COS etc.) Yes Yes Yes Yes Yes
Hyperbolic trig. (SINH, COSH etc.) + - - - -
# of trig. modes (degrees, radians, grads) 3 3 3 3 3
Advanced Math HP-65 HP-55 HP-25 HP-29C HP-45
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 HP-29C HP-45
Mean, standard deviation (# of variables) + 2 1 2 1
Σ of n, x, x2 + Yes Yes Yes Yes
Σ of n, x, x2, y + Yes Yes Yes Yes
Σ of n, x, x2, y, xy + Yes Yes Yes -
Σ of n, x, x2, y, y2, xy + Yes - Yes -
Σ of lists - - - - -
Random number generator + - - - -
Linear regression, estimate  + Yes - - -
Curve fitting + - - - -
Correlation coefficient + - - - -
Normal distribution + - - - -
Factorial Yes Yes - - Yes
Gamma - - - - -
Combinations and permutations + - - - -
Scientific and Time HP-65 HP-55 HP-25 HP-29C HP-45
Polar / rectangular conversions Yes Yes 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 Yes Yes
Hrs.min.sec arithmetic Yes Yes - - -
Time of day clock - - - - -
Timer - Yes - - Unofficial
Dynamic calculations (timer × rate) - - - - -
Alarms - - - - -
Unit Conversions HP-65 HP-55 HP-25 HP-29C HP-45
Centimeters / inches some - - - Yes
Millimeters / inches - Yes - - -
Meters / feet - Yes - - -
Kilograms / pounds (mass) - Yes - - Yes
Newtons / pounds (force) - Yes - - -
British thermal units / joules - Yes - - -
Liters / gallons - Yes - - Yes
° Celsius / ° Fahrenheit - Yes - - -
Other - - - - -
User-defined units - - - - -
Time Value of Money HP-65 HP-55 HP-25 HP-29C HP-45
Number of payments (n) + - - - -
Interest rate (i) + - - - -
Present Value (PV) + - - - -
Payment (PMT) + - - - -
Future Value (FV) + - - - -
Cash Flow Analysis HP-65 HP-55 HP-25 HP-29C HP-45
Net present value (NPV) + - - - -
Internal rate of return (IRR) + - - - -
Amortization HP-65 HP-55 HP-25 HP-29C HP-45
Accumulated Interest (ACC INT) + - - - -
Balance (BAL) + - - - -
Depreciation HP-65 HP-55 HP-25 HP-29C HP-45
Straight line (SL) + - - - -
Sum of the years digits (SOYD) + - - - -
Declining balance (DB) + - - - -
Bonds and calendar functions HP-65 HP-55 HP-25 HP-29C HP-45
Bond price + - - - -
Bond yield + - - - -
Date arithmetic / calendar functions + - - - -
Memory and Programming HP-65 HP-55 HP-25 HP-29C HP-45
Programming language(s) RPN RPN RPN RPN -
RAM / Max # of variables or addressable registers 9 Registers 20 Registers 8 Registers 30 Registers 9 Registers
Max # of program steps 100 50 49 98 -
RAM / Max vars or regs with full optional RAM - - - - -
Max # of prog steps with full optional RAM - - - - -
Merged program steps  Partially - Yes Yes -
Manual register / program memory allocation  - - - - -
Automatic register / program memory allocation - - - - -
Overlapped register and program memory - - - - -
Continuous memory - - - Yes* -
Flags 2 - - - -
Conditional tests 4 2 8 8 -
Subroutine levels 1 - - 3 -
Indexed looping (increment by +/- 1, end at 0) Yes - - Yes -
Indexed looping (choice of increment and end) - - - - -
Multiple index / loop registers - - - - -
Line number addressing - - Yes - -
Branching by relative line number - - - Yes -
Global program label addressing Yes - - Yes -
Local program label addressing - - - - -
Indirect / computed addressing and control - - - Yes -
Multiple indirection registers - - - - -
Pause - - Yes Yes -
Alpha messages and prompts in programs - - - - -
Alpha program listings - - - - -
Alpha string manipulation - - - - -
Program step insert / delete Yes - - Yes -
I/O and Expansion Features HP-65 HP-55 HP-25 HP-29C HP-45
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 HP-29C HP-45
Sounds - - - - -
Self test - - - - -
Hard case (in addition to soft case) Yes Yes - - Yes
Additional Features - - - - -
Batteries Rechargeable Rechargeable Rechargeable Rechargeable Rechargeable
Length (inches) 6.0" 5.8" 5.1" 5.1" 5.8"
Width 3.2" 3.2" 2.7" 2.7" 3.2"
Height 1.4" 1.3" 1.2" 1.2" 1.3"
Weight (oz or lbs) 11 oz 8.7 oz 6 oz 6 oz 8.7 oz
Year of introduction 1974 1975 1975 1977 1973
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.
HP-29C notes:
  • The HP-19C has its own features page.
  • 16 of the 30 registers were continuous.
HP-45 notes:
  • Most (possibly all) HP-45's had the code for the timer found in the HP-55. See the HP-45 page for details.
  • This model supplied conversion factors rather than conversions. The 3 constants could be multiplied or divided to perform 6 conversions.

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