The Museum of HP Calculators


HP-55 Features

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
Display type LED
Display format 1 Line
FIXed number format Yes
SCIentific number format Yes
ENGineering number format -
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
Logic system RPN
Stack levels 4
Last x Yes
Undo -
Precedence -
Parentheses -
Storage Addition (STO +) -
Storage Arithmetic (STO +, -, ×, ÷) -
Storage Exponentiation (STO ^) -
Recall Arithmetic -
Named variables -
Multiple data types -
Directories -
   
Math HP-55
+, -, ×, ÷ Yes 
1/x Yes
sq. root Yes
x2 Yes
LOG x Yes
10x Yes
LN x Yes
ex Yes
yx Yes
pi Yes
% Yes
% change -
INTeger truncation and ABSolute value -
Trigonometric functions (SIN, COS etc.) Yes
Hyperbolic trig. (SINH, COSH etc.) -
# of trig. modes (degrees, radians, grads) 3
   
Advanced Math HP-55
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
Mean, standard deviation (# of variables) 2
Summation of n, x, x2 Yes
Summation of n, x, x2, y Yes
Summation of n, x, x2, y, xy 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

Polar / rectangular conversions 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
Hrs.min.sec arithmetic Yes
Time of day clock -
Timer Yes
Dynamic calculations (timer × rate) -
Alarms -
   
Unit Conversions

HP-55

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

-

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

-

Overlapped register and program memory -
Continuous memory

-

Flags -
Conditional tests 2
Subroutine levels -
Indexed looping (increment by +/- 1, end at 0) -
Indexed looping (choice of increment and end) -
Multiple index / loop registers -
Line number addressing -
Branching by relative line number -
Global program label addressing -
Local program label addressing -
Indirect / computed addressing and control -
Multiple indirection registers -
Pause -
Alpha messages and prompts in programs -
Alpha program listings -
Alpha string manipulation -
Program step insert / delete -
   
I/O and Expansion Features HP-55
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
Sounds -
Self test -
Hard case (in addition to soft case) Yes
Additional Features -
Batteries Rechargeable
Length (inches) 5.8"
Width 3.2"
Height 1.3"
Weight (oz or lbs) 8.7 oz
Year of introduction 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.

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