Hewlett-Packard HP-22S

Datasheet legend
Ab/c: Fractions calculation
AC: Alternating current
BaseN: Number base calculations
Card: Magnetic card storage
Cmem: Continuous memory
Cond: Conditional execution
Const: Scientific constants
Cplx: Complex number arithmetic
DC: Direct current
Eqlib: Equation library
Exp: Exponential/logarithmic functions
Fin: Financial functions
Grph: Graphing capability
Hyp: Hyperbolic functions
Ind: Indirect addressing
Intg: Numerical integration
Jump: Unconditional jump (GOTO)
Lbl: Program labels
LCD: Liquid Crystal Display
LED: Light-Emitting Diode
Li-ion: Lithium-ion rechargeable battery
Lreg: Linear regression (2-variable statistics)
mA: Milliamperes of current
Mtrx: Matrix support
NiCd: Nickel-Cadmium rechargeable battery
NiMH: Nickel-metal-hydrite rechargeable battery
Prnt: Printer
RTC: Real-time clock
Sdev: Standard deviation (1-variable statistics)
Solv: Equation solver
Subr: Subroutine call capability
Symb: Symbolic computing
Tape: Magnetic tape storage
Trig: Trigonometric functions
Units: Unit conversions
VAC: Volts AC
VDC: Volts DC
Years of production: 1988-1991 Display type: Numeric display  
New price: USD 60.00   Display color: Black  
    Display technology: Liquid crystal display 
Size: 6"×3"×½" Display size: 12(9+2) digits
Weight: 6 oz    
    Entry method: Algebraic with precedence 
Batteries: 3×"LR44" button cell Advanced functions: Trig Exp Hyp Lreg Solv Cmem BaseN Units Eqlib 
External power:   Memory functions: +/-/×/÷ 
I/O: IR output     
    Programming model: Formula programming 
Precision: 12 digits Program functions:  
Memories: 371(0) bytes Program display: Formula display  
Program memory: 371 bytes Program editing: Formula entry  
Chipset: Saturn   Forensic result:  

hp22s.jpg (26731 bytes)The HP-22S belongs to the Pioneer series of Hewlett-Packard's line of calculators. Although it is a close relative to the HP-20S and HP-21S, it is not a keystroke-programmable machine; instead, it has a built-in "SOLVE" function that lets you enter equations in algebraic form and solve for unknown variables. Since this SOLVE feature also has the capability to evaluate formulae, this makes the HP-22S technically a programmable machine; you can enter a mathematical expression which is then stored permanently in the calculator's continuous memory, and you can evalute the expression at a later time.

Whereas some other Hewlett-Packard calculators with a similar SOLVE feature offer special functions for conditional execution or loops, these functions are not present in the HP-22S. Therefore, this calculator is limited to more straightforward formulae. That said, I was suprised to find that the machine has sufficient storage for an implementation of my favorite example, the Gamma function, with plenty of memory to spare.


Looks ugly, but it works! Better yet, thanks to the built-in SOLVE feature, we automatically get an inverse Gamma function as well. Instead of specifying X and solving for G, you can specify G and solve for X; for instance, you can determine that the Gamma function's value is exactly 100 for 5.89251869634.