A slim, elegant, and useful model, the Canon F-73P is a nice example of a programmable scientific calculator. That despite the fact that its programming model is somewhat limited: 45 partially merged steps isn't a great deal of program memory, and the inability to edit/view programs is annoying.

That said, 45 partially merged steps can be quite useful, especially when the calculator does offer limited decision-making capabilities: in the case of the F-73P, the ability to execute conditional and unconditional jumps within the code. In fact, it is this what distinguishes a true computer from a mere automaton; I guess the F-73P would qualify as a device banned by the Great Convention in Frank Herbert's immortal Dune!

The chipset of the F-73P is used in other calculators. I first came across a similar model when my friend Joerg Woerner sent me a Citizen SR-59. At first, I found the programming model too limited, too constraining; eventually, however, I was able to squeeze even complex algorithms into this machine's memory, including the following iterative program for the incomplete Gamma function:

01:  STO
02:  2
03:  RM
04:  STO
05:  1
06:  ax
07:  RCL
08:  2
09:  ÷
10:  RCL
11:  1
12:  ex
13:  ÷
14:  RCL
15:  2
16:  =
17:  STO
18:  3
19:  SM
20:  RCL
21:  3
22:  ×
23:  RCL
24:  1
25:  ÷
26:  (
27:  GOTO 1
28:  GOTO -9
29:  RCL
30:  2
31:  +
32:  1
33:  )
34:  STO
35:  2
36:  GOTO 1
37:  GOTO -9
38:  +
39:  STO
40:  3
41:  RM
42:  =
43:  x<=M 1
44:  GOTO -7
45:  RM