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-55 HP-25
Display type LED LED
Display format 1 Line 1 Line
FIXed number format Yes Yes
SCIentific number format Yes Yes
ENGineering number format - Yes
STanDard / ALL number format - -
Alpha messages and prompts - -
Softkeys labeled by mag. card or overlay - -
Softkeys labeled by display menus - -
Softkeys with neither labeling system - -
Status annunciators - -
Redefinable keyboard - -
     
Logic HP-55 HP-25
Logic system RPN RPN
Stack levels 4 4
Last x Yes 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-55 HP-25
+, -, ×, ÷ Yes  Yes 
1/x Yes Yes
sq. root Yes Yes
x2 Yes Yes
LOG x Yes Yes
10x Yes Yes
LN x Yes Yes
ex Yes Yes
yx Yes Yes
pi Yes Yes
% Yes Yes
% change - -
INTeger truncation and ABSolute value - Yes
Trigonometric functions (SIN, COS etc.) Yes Yes
Hyperbolic trig. (SINH, COSH etc.) - -
# of trig. modes (degrees, radians, grads) 3 3
     
Advanced Math HP-55 HP-25
Solver / root finder - -
Numeric integration - -
Complex numbers - -
Matrix operations - -
Matrix writer - -
Equation writer - -
Symbolic operations - -
Fractions - -
Plotting and graphics (display) - -
Plotting and graphics (printer / plotter) - -
     
Statistical HP-55 HP-25
Mean, standard deviation (# of variables) 2 1
Summation of n, x, x2 Yes Yes
Summation of n, x, x2, y Yes Yes
Summation of n, x, x2, y, xy Yes Yes
Summation of n, x, x2, y, y2, xy Yes -
Summation 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-55

HP-25

Polar / rectangular conversions Yes Yes
Base conversions (2, 8, 10, 16) - -
Arithmetic in bases 2, 8 and 16 - -
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
Hrs.min.sec arithmetic Yes -
Time of day clock - -
Timer Yes -
Dynamic calculations (timer × rate) - -
Alarms - -
     
Unit Conversions

HP-55

HP-25

Centimeters / inches - -
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-55 HP-25
Number of payments (n) - -
Interest rate (i) - -
Present Value (PV) - -
Payment (PMT) - -
Future Value (FV) - -
     
Cash Flow Analysis HP-55 HP-25
Net present value (NPV) - -
Internal rate of return (IRR) - -
     
Amortization HP-55 HP-25
Accumulated Interest (ACC INT) - -
Balance (BAL) - -
     
Depreciation HP-55 HP-25
Straight line (SL) - -
Sum of the years digits (SOYD) - -
Declining balance (DB) - -
     
Bonds and calendar functions HP-55 HP-25
Bond price - -
Bond yield - -
Date arithmetic / calendar functions - -
     
Memory and Programming HP-55 HP-25
Programming language(s) RPN RPN
RAM / Max # of variables or addressable registers 20 Registers 8 Registers
Max # of program steps 50 49
RAM / Max vars or regs with full optional RAM - -
Max # of prog steps with full optional RAM - -
Merged program steps 

-

Yes

Manual register / program memory allocation  - -
Automatic register / program memory allocation

-

-

Overlapped register and program memory - -
Continuous memory

-

-

Flags - -
Conditional tests 2 8
Subroutine levels - -
Indexed looping (increment by +/- 1, end at 0) - -
Indexed looping (choice of increment and end) - -
Multiple index / loop registers - -
Line number addressing - Yes
Branching by relative line number - -
Global program label addressing - -
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 - -
     
I/O and Expansion Features HP-55 HP-25
ROM modules - -
RAM modules or expansion option - -
General expansion slots / connector - -
Magnetic card reader/writer - -
Tape drive - -
Disk drive - -
Upgradeable firmware - -
Optical wand - -
Serial port - -
Infrared input - -
Infrared output - -
Printer - -
Networking - -
Other - -
     
General HP-55 HP-25
Sounds - -
Self test - -
Hard case (in addition to soft case) Yes -
Additional Features - -
Batteries Rechargeable Rechargeable
Length (inches) 5.8" 5.1"
Width 3.2" 2.7"
Height 1.3" 1.2"
Weight (oz or lbs) 8.7 oz 6 oz
Year of introduction 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.

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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