Radio Shack EC-4001

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: 1977  Display type: Numeric display  
New price:   Display color: Red  
    Display technology: Light-emitting diode 
Size: 4½"×2"×1" Display size: 8(5+2) digits
Weight: 4 oz    
    Entry method: Algebraic 
Batteries: 1×9V alkaline Advanced functions: Trig Exp 
External power: Sinclair Mains Adaptor   Memory functions:  
    Programming model: Keystroke entry 
Precision: 8 digits Program functions: Jump Cond  
Memories: 1 numbers Program display: Keycode display  
Program memory: 36 program steps Program editing: Overwrite capability  
Chipset: Sinclair Cambridge Programmable   Forensic result:  

*Built-in scientific functions are highly inaccurate, some yielding only 3 significant digits

ec4001.jpg (11527 bytes)The EC-4001 was the second programmable calculator bearing the Radio Shack store brand name. Whereas the EC-4000 was an OEM version of the Texas Instruments TI-57, the EC-4001 is a legendary British calculator in disguise: the Sinclair Cambridge Programmable.

Thirty-six program steps and a single memory register are not a heck of a lot. On the other hand, for a price that was a fraction of what you paid for other programmable pocket calculators, you got yourself a useful machine in a very tiny package. Along with the machine an extensive printed library of programs was supplied, containing more than a hundred applications from various fields of discipline.

One major problem (apparently affecting other Sinclair products of the time as well) is that this little machine is, quite frankly, a little sloppy. I don't just mean the low quality plastic construction, but also the fact that its internal mathematical algorithms are astonishingly inaccurate. For certain (supposedly valid) arguments, trigonometric functions only yield three significant digits of precision! An experienced engineer with a good slide rule could do better than that..

So here is an inaccurate program for an inaccurate machine: an approximation of the Gamma function's logarithm using Stirling's formula. In fact, this program is actually more accurate for most arguments than built-in trigonometric functions, so who needs anything better?

00    sto   2
01    -     F
02    #     3
03    .     A
04    5     5
05    ×     .
06    (     6
07    rcl   5
08    ln    4
09    )     6
10    -     F
11    rcl   5
12    +     E
13    #     3
14    .     A
15    9     9
16    1     1
17    8     8
18    9     9
19    3     3
20    8     8
21    5     5
22    +     E
23    (     6
24    #     3
25    1     1
26    2     2
27    ÷     G
28    ÷     G
29    rcl   3
30    )     6
31    =     -
32    stop  0