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

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