Hewlett-Packard HP-28C

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: 1988-1989 Display type: Graphical display  
New price: USD 235.00   Display color: Black  
    Display technology: Liquid crystal display 
Size: 6"×8"×½" Display size: 137×32 pixels
Weight: 8 oz    
    Entry method: Reverse Polish Notation 
Batteries: 3×"N" alkaline Advanced functions: Trig Exp Hyp Lreg Grph Solv Intg Ab/c Cplx Symb Cmem RTC Snd Mtrx BaseN Units Const 
External power:   Memory functions: +/-/×/÷ 
I/O: IR output     
    Programming model: Reverse Polish Language 
Precision: 12 digits Program functions: Jump Cond Subr Lbl Ind  
Memories: 2(0) kilobytes Program display: Text display  
Program memory: 2 kilobytes Program editing: Text editor  
Chipset: Saturn   Forensic result: 8.99999864267  

hp28c.jpg (52320 bytes)The HP-28C was a short-lived version of Hewlett Packard's more popular HP-28S calculator. Unlike the HP-28S with its 32 kB of RAM, the HP-28C had only a miserable 2 kB. Otherwise, the two calculators were identical.

According to calculator folklore,  HP quickly realized that only 2 kB of memory is simply not enough to take advantage of the amazing capabilities this machine has to offer. Which is why, shortly after its introduction, the 28C was replaced with the 28S and disappeared form store shelves. Which may explain why this calculator is a bit difficult to find nowadays.

Well, on a calculator with too little memory, it only makes sense to save some, even if it's at the expense of processing time. So rather than presenting yet another copy of my usual Gamma function programming example, here's a program that calculates the incomplete Gamma function. This program can also be used to approximate the regular Gamma function by specifying a high enough integration limit; for instance, 5 ENTER 50 IGAMMA (assuming the program is saved under the name IGAMMA) yields 24, the exact value of the Gamma function of 5.

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