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APF Mark 231

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*memory backup only

Here's a desktop calculator that would not normally belong to my collection but it is too unusual to be left out. The APF 231 looks like your standard old-style heavy-duty electronic business calculator, until you look closer and realize that it's a little bit more than that; it is actually a programmable old-style heavy-duty electronic business calculator!

Programming, in this case, means recording up to 9 keyboard macros, to a combined length of up to 256 keystrokes. That's a fair bit of storage but in the absence of program editing functions, conditional or unconditional branching, or the ability to call programs as subprograms from within another program, the machine's program capability is more limited than it should be. On the plus side, program memory is protected by an internal NiCd battery.

No exponential functions, no logarithms, and no subprogram capability means it is unlikely that I'll ever be able to implement my favorite example on this machine, the Gamma function. But that doesn't mean that sophisticated algorithms cannot be keyed in on this machine as long as you have the patience to do it. Case in question: the program below actually calculates the sign of any angle (expressed in radians) using a polynomial approximation. There you go, trigonometric functions on a programmable four-banger!

Switch Settings
Float
Day OFF
Fn OFF
5/4
SIGMA ON
IC OFF
NP

000   LB
001   M+=
002   +
003   ×
004   =
005   =
006   ÷
007   K
008   2
009   ÷
010   K
011   3
012   =
013   MII
014   M+=
015   -
016   MR
017   ×
018   MII
019   MC
020   =
021   =
022   ÷
023   K
024   4
025   ÷
026   K
027   5
028   =
029   MII
020   M+=
031   +
032   MR
033   ×
034   MII
035   MC
036   =
037   =
038   ÷
039   K
040   6
041   ÷
042   K
043   7
044   =
045   MII
046   M+=
047   -
048   MR
049   ×
050   MII
051   MC
052   =
053   =
054   ÷
055   K
056   8
057   ÷
058   K
059   9
060   =
061   MII
062   M+=
063   +
064   MR
065   ×
066   MII
067   MC
068   =
069   =
070   ÷
071   K
072   1
073   0
074   ÷
075   K
076   1
077   1
078   =
079   MII
080   M+=
081   -
082   MR
083   ×
084   MII
085   MC
086   =
087   =
088   ÷
089   K
090   1
091   2
092   ÷
093   K
094   1
095   3
096   =
097   MII
098   M+=
099   +
100   MR
101   ×
102   MII
103   MC
104   =
105   =
106   ÷
107   K
108   1
109   4
110   ÷
111   K
112   1
113   5
114   =
115   MII
116   M+=
117   -
118   MC
119   ×
120   MII
121   MC
122   =
123   =
124   ÷
125   K
126   1
127   6
128   ÷
129   K
130   1
131   7
132   =
133   +
134   T
135   LB