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Casio FX-602P

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Despite the prodigious number of calculator models Casio produced over the years, few are inspiring. This early LCD model, the FX-602P, is, however, an exception. A very well designed machine with considerable memory capacity, the FX-602P has a good programming model, several program control instructions, even something that's an absolute rarity on Casio calculators: indirect memory access.

One thing that this machine curiously lacks is display contrast control. (Unless there's some obscure key combination for it, described in a manual I do not have.) It took some time until I found an internal potentiometer that helped me turn down the display contrast; initially, the display was so dark, it was nearly unreadable.

Needless to say, as soon as I had a readable display, I began playing with my new calculator; and my playing, as usual, included writing another program for the Gamma function. This 82-step program neatly demonstrates the calculator's programming model, as it calculates the natural logarithm of the Gamma function for all real arguments to 10+ digits of precision:

001	Min00
002	1
003	Min01
004	5
005	MinF
006	LBL1
007	MR00
008	x>=F
009	GOTO2
010	MR00
011	×
012	MR01
013	=
014	Min01
015	1
016	M+00
017	GOTO1
018	LBL2
019	MR00
020	×
021	ln
022	-
023	MR00
024	+
025	(
026	2
027	×
028	
029	÷
030	MR00
031	)
032	
033	ln
034	+
035	(
036	(
037	(
038	(
039	9
040	9
041	1/x
042	÷
043	MR00
044	x2
045	-
046	1
047	4
048	0
049	1/x
050	)
051	÷
052	MR00
053	x2
054	+
055	1
056	0
057	5
058	1/x
059	)
060	÷
061	MR00
062	x2
063	-
064	3
065	0
066	1/x
067	)
068	÷
069	MR00
070	x2
071	+
072	1
073	)
074	÷
075	1
076	2
077	÷
078	MR00
079	-
080	MR01
081	ln
082	=