Third time lucky, they say. Twice before, I bought a dysfunctional HP-29C calculator, only to find out that I am unable to repair them; not even swapping suspect chips was sufficient to bring even one of them back to life.

The third time was different; recently I acquired an HP-29C that was reported to be non-functional by its owner, and to my delight, I found that after inserting a new battery pack, the machine came to life and has been working flawlessly ever since.

The HP-29C is the non-printing twin to Hewlett-Packard's HP-19C. Both machines are beautiful examples of calculator engineering. They are high-end programmables, quite capable machines with 98 fully merged program steps and 30 memory registers. All program steps and most memory registers are preserved when the calculator is powered down. The HP-19C is probably the smallest printing programmable calculator ever produced; the HP-29C, in turn, is probably the smallest high-end programmable (and one of the smallest programmables overall) ever manufactured.

These machines are a real pleasure to use. Even after 22 years, the keys are crisp and bounce-free, the programming model is sophisticated, elegant, and efficient, and the machine just feels good in one's hands.

My favorite programming example, of course, is the Gamma function, which I already implemented for the HP-19C. However, it is worth repeating here, if only because, although the two calculators share the same programming model, their numeric keycodes are different. Remember: in order to use this program, it is necessary to first populate registers 1-7 with the values shown here.

M1:    76.18009173
M2:    -86.50532033
M3:    24.01409824
M4:    -1.231739572
M5:    1.208650974e-3
M6:    -5.395239385e-6
M7:    √2π = 2.506628275

01  15 13 00	LBL 0
02  01		1
03  21		x-y
04  15 13 02	LBL 2
05  00		0
06  14 41	x<=y
07  13 01	GTO 1
08  22		Rv
09  31		ENTER
10  22		Rv
11  61		×
12  22		Rv
13  22		Rv
14  22		Rv
15  01		1
16  51		+
17  13 02	GTO 2
18  15 13 01	LBL 1
19  22		Rv
20  23 09	STO 9
21  21		x-y
22  23 08	STO 8
23  06		6
24  23 00	STO 0
25  01		1
26  15 13 03	LBL 3
27  24 22	RCL i
28  24 09	RCL 9
29  24 00	RCL 0
30  51		+
31  71		÷
32  51		+
33  15 23	DSZ
34  13 03	GTO 3
35  24 07	RCL 7
36  61		×
37  24 09	RCL 9
38  71		÷
39  14 42	ln
40  24 09	RCL 9
41  05		5
42  73		.
43  05		5
44  51		+
45  14 42	ln
46  24 09	RCL 9
47  73		.
48  05		5
49  51		+
50  61		×
51  51		+
52  24 09	RCL 9
53  41		-
54  05		5
55  73		.
56  05		5
57  41		-
58  15 42	ex
59  24 08	RCL 8
60  71		÷
61  15 12	RTN