Features in optional ROMs are listed as Option. 

Display and Keyboard  HP 9815S 
Display type  Gas Plasma 
Display format  1 Line 
FIXed number format  Yes 
SCIentific number format  Yes 
ENGineering number format  Yes* 
STanDard / ALL number format   
Alpha messages and prompts  On printer 
Softkeys labeled by mag. card or overlay  Yes 
Softkeys labeled by display menus   
Softkeys with neither labeling system   
Status annunciators   
Redefinable keyboard   
Logic  HP 9815S 
Logic system  RPN 
Stack levels  4 
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 9815S 
+, , ×, ÷  Yes 
1/x  Yes 
sq. root  Yes 
x^{2}  Yes 
LOG x  Yes 
10^{x}  Yes 
LN x  Yes 
e^{x}  Yes 
y^{x}  Option 
pi  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)  3 
Advanced Math  HP 9815S 
Solver / root finder   
Numeric integration   
Complex numbers  Limited 
Matrix operations   
Matrix writer   
Equation writer   
Symbolic operations   
Fractions   
Plotting and graphics (display)   
Plotting and graphics (printer / plotter)  Option 
Statistical  HP 9815S 
Mean, standard deviation (# of variables)  1 
Summation of n, x, x^{2}  Yes 
Summation of n, x, x^{2}, y   
Summation of n, x, x^{2}, y, xy   
Summation of n, x, x^{2}, y, y^{2}, xy   
Summation of lists   
Random number generator   
Linear regression, estimate   
Curve fitting   
Correlation coefficient   
Normal distribution   
Factorial   
Gamma   
Combinations and permutations   
Scientific and Time  
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 (164 bits)   
Selectable complement mode (1's, 2's, unsigned)   
Decimal hrs / hrs.min.sec. conversions  Yes 
Hrs.min.sec arithmetic   
Time of day clock   
Timer   
Dynamic calculations (timer × rate)   
Alarms   
Unit Conversions  
Centimeters / inches   
Millimeters / inches   
Meters / feet   
Kilograms / pounds (mass)   
Newtons / pounds (force)   
British thermal units / joules   
Liters / gallons   
° Celsius / ° Fahrenheit   
Other   
Userdefined units   
Time Value of Money  HP 9815S 
Number of payments (n)   
Interest rate (i)   
Present Value (PV)   
Payment (PMT)   
Future Value (FV)   
Cash Flow Analysis  HP 9815S 
Net present value (NPV)   
Internal rate of return (IRR)   
Amortization  HP 9815S 
Accumulated Interest (ACC INT)   
Balance (BAL)   
Depreciation  HP 9815S 
Straight line (SL)   
Sum of the years digits (SOYD)   
Declining balance (DB)   
Bonds and calendar functions  HP 9815S 
Bond price   
Bond yield   
Date arithmetic / calendar functions   
Memory and Programming  HP 9815S 
Programming language(s)  RPN 
RAM / Max # of variables or addressable registers  256 
Max # of program steps  3800 
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  Yes 
Automatic register / program memory allocation   
Overlapped register and program memory   
Continuous memory   
Flags  8 
Conditional tests  3 
Subroutine levels  7 
Indexed looping (increment by +/ 1, end at 0)   
Indexed looping (choice of increment and end)  Yes 
Multiple index / loop registers  Yes 
Line number addressing  Yes 
Branching by relative line number   
Global program label addressing  Yes 
Local program label addressing   
Indirect / computed addressing and control  Yes 
Multiple indirection registers  Yes 
Pause  Yes 
Alpha messages and prompts in programs  On printer 
Alpha program listings  Yes 
Alpha string manipulation   
Program step insert / delete  Yes 
I/O and Expansion Features  HP 9815S 
ROM modules   
RAM modules or expansion option  Yes 
General expansion slots / connector  Yes 
Magnetic card reader/writer   
Tape drive  Yes 
Disk drive   
Upgradeable firmware   
Optical wand   
Serial port   
Infrared input   
Infrared output   
Printer  Yes 
Networking  HPIB Option 
Other  Digitizer, plotter, 2 paper tape readers, tape punch, pagewidth printer, BCD, GPIO, etc. 
General  HP 9815S 
Sounds   
Self test   
Hard case (in addition to soft case)  Yes 
Additional Features   
Batteries   
Length (inches)  13.5" 
Width  13.75" 
Height  4.1" 
Weight (oz or lbs)  12 lbs 
Year of introduction  1976 
Features in optional ROMs are listed as Option. 
HP 9815S notes:

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