The year is 1973. The war in Vietnam is winding down. The Organization of Petroleum Exporting Countries imposes a ban on oil exports to the United States. The UPC (Universal Product Code) bar code standard is established. The US Department of Defense develops a new internetwork protocol, called TCP/IP. Apollo no longer flies to the Moon, but Pioneer 10 flies by Jupiter, and the Soviet Union resumes the Soyuz program after a tragic loss of three cosmonauts a year earlier. And a little boy from Hungary visits an aunt in Canada, telling every family friend and relative that he wants a "pocket calculator". Finally, somebody relents and buys him one... a mechanical contraption operated with a stylus. What the boy wanted of course was an electronic pocket calculator; little did he know that a bunch of engineers at Hewlett-Packard's Advanced Products Division in Corvallis, Oregon, were already working on something much more than that. Their next product, introduced early in the following year, was the first practical example of "wearable computing": a pocketable device with programmability, and permanent storage of programs and data on tiny magnetic cards.

The HP-65, introduced in 1974, was the first ever programmable handheld calculator; and what a calculator it is! A full complement of scientific functions, 100 partially merged program steps, 9 memories, labels, conditional branching, subroutines, simple program editing capability (inserting and deleting steps), and to top it all off, a magnetic card reader for recording programs. This calculator is nothing short of a stunning engineering achievement.

I now have one of these units and I even managed to get its card reader to work reliably. Needless to say, I am quite happy! There is something absolutely magical about it, when a 25-year old piece of hardware that includes mechanical parts still works the way its designers intended. Mind you, the fact that this, the world's first programmable pocket calculator, is still an eminently useful device in 1999, is no less amazing.

One result of my experimentation with this little marvel is yet another implementation of the Gamma function. This program is a little bit inelegant in that it requires 6 registers to be initialized by the user with preset values. Then again, a separate program can be created (and perhaps recorded on the back side of a magnetic card) that sets the values in these registers.

The program calculates the Gamma function for any real argument for which the function has a value. To use it, enter the argument and hit the A button.

M3: 83.86760434
M4: 1168.926495
M5: 8687.245297
M6: 36308.29515
M7: 80916.62790
M8: 75122.63315

00 23     LBL
01 11     A
02 01     1
03 35 02  STO 2
04 35 08  Rv
05 23     LBL
06 01     1
07 00     0
08 35 22  x<=y
09 22     GTO
10 02     2
11 35 08  Rv
12 33     STO
13 71     ×
14 02     2
15 01     1
16 61     +
17 22     GTO
18 01     1
19 23     LBL
20 02     2
21 35 08  Rv
22 33 01  STO 1
23 02     2
24 35     g
25 02     π
26 71     ×
27 31     f
28 09     √
29 71     ×
30 34 03  RCL 3
31 61     +
32 34 01  RCL 1
33 71     ×
34 34 04  RCL 4
35 61     +
36 34 01  RCL 1
37 71     ×
38 34 05  RCL 5
39 61     +
40 34 01  RCL 1
41 71     ×
42 34 06  RCL 6
43 61     +
44 34 01  RCL 1
45 71     ×
46 34 07  RCL 7
47 61     +
48 34 08  RCL 8
49 34 01  RCL 1
50 81     ÷
51 61     +
52 34 01  RCL 1
53 01     1
54 61     +
55 81     ÷
56 34 01  RCL 1
57 02     2
58 61     +
59 81     ÷
60 34 01  RCL 1
61 03     3
62 61     +
63 81     ÷
64 34 01  RCL 1
65 04     4
66 61     +
67 81     ÷
68 34 01  RCL 1
69 05     5
70  61     +
71 81     ÷
72  34 01  RCL 1
73 06     6
74 61     +
75 81     ÷
76 34 01  RCL 1
77 05     5
78 83     .
79 05     5
80 61     +
81 34 01  RCL 1
82 83     .
83 05     5
84 61     +
85 35     g
86 05     yx
87 71     ×
88 34 01  RCL 1
89 05     5
90 83     .
91 05     5
92 61     +
93 32     f−1
94 07     LN
95 81     ÷
96 34 02  RCL 2
97 81     ÷
98 24     RTN
99 35 01  NOP

Initialization program (hit E to execute):

00 23     LBL
01 11     E
02 08     8
03 03     3
04 83     .
05 08     8
06 06     6
07 07     7
08 06     6
09 00     0
10 04     4
11 03     3
12 04     4
13 33 03  STO 3
14 01     1
15 01     1
16 06     6
17 08     8
18 83     .
19 09     9
20 02     2
21 06     6
22 04     4
23 09     9
24 05     5
25 33 04  STO 4
26 08     8
27 06     6
28 08     8
29 07     7
30 83     .
31 02     2
32 04     4
33 05     5
34 02     2
35 09     9
36 07     7
37 33 05  STO 5
38 03     3
39 06     6
40 03     3
41 00     0
42 08     8
43 83     .
44 02     2
45 09     9
46 05     5
47 01     1
48 05     5
49 33 06  STO 6
50 08     8
51 00     0
52 09     9
53 01     1
54 06     6
55 83     .
56 06     6
57 02     2
58 07     7
59 09     9
60 33 07  STO 7
61 07     7
62 05     5
63 01     1
64 02     2
65 02     2
66 83     .
67 06     6
68 03     3
69 03     3
70 01     1
71 05     5
72 33 08  STO 8
73 31     f
74 42     STK
75 24     RTN
76 35 01  NOP
77 35 01  NOP
78 35 01  NOP
79 35 01  NOP
80 35 01  NOP
81 35 01  NOP
82 35 01  NOP
83 35 01  NOP
84 35 01  NOP
85 35 01  NOP
86 35 01  NOP
87 35 01  NOP
88 35 01  NOP
89 35 01  NOP
90 35 01  NOP
91 35 01  NOP
92 35 01  NOP
93 35 01  NOP
94 35 01  NOP
95 35 01  NOP
96 35 01  NOP
97 35 01  NOP
98 35 01  NOP
99 35 01  NOP