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.

G=SQRT(2×π)÷X×(1.00000000019+
   76.1800917295÷(X+1)-86.5053203294÷(X+2)+
   24.0140982408÷(X+3)-1.23173957245÷(X+4)+
   1.20865097387E-3÷(X+5)-5.39523938495E-6÷(X+6))×
   (X+5.5)^(X+.5)÷EXP(X+5.5)

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.