During a recent trip to Hungary, my wife visited a flea market. That evening when we spoke on the telephone, she told me excitedly that she found some interesting-looking old calculators. One of them had a model number that was a bit faded and hard to read; a PTK... what, 1058? No, it must be a 1050! Yippie! Another rare model, finally located.

I have no idea really how rare the PTK-1050 was, but I certainly didn't encounter it back when it was originally manufactured. It was only much later that I learned about this model number and found out that it was none other but the Texas Instruments TI-57 in disguise (this, in fact, is visible in the picture on the right, as the original Texas Instruments label is faintly revealed under the fading Hungarian overlay.) A good calculator it is, too; its limited program capacity is offset by its fully merged programming model (this was the only early Texas Instruments calculator with this feature) and a well-designed set of program instructions. The only shortcoming is the lack of permanent program storage or continuous memory, making it necessary to re-enter programs every time the calculator is turned off.

Alas, when I powered up this PTK-1050, it was just barely functional. The display came up alright, but half the keyboard was dead, not responding at all to keystrokes. Opening the calculator quickly revealed the cause: the keyboard panel was thoroughly rotten with corrosion.

Fortune intervened. Just recently, I acquired a set of what appeared to be Texas Instruments keyboard panels. And that's indeed what they were: keyboard panels for the TI-59 family of calculators. The good news is that these keyboard panels are essentially identical to those used in the TI-57, except for an extra row of keys at the top. This row of keys can be carefully removed without damaging the connecting wires or the remainder of the keyboard. Which is exactly what I did, and after less than an hour of surgery, I had a fully functional PTK-1050 in my hands.

The program below demonstrates the power of this calculator by implementing the Gamma function using the Lanczos-approximation, computing the logarithm of the Gamma function to the maximum achievable precision for all positive arguments.

M0=2.5066282835
M1=92.207048452
M2=-83.177637083
M3=14.802831931
M4=-0.22084970795

00  86 0   LBL 0
01  38 1   EXC 1
02  45     ÷
03  38 1   EXC 1
04  32 5   STO 5
05  75     +
06  33 0   RCL 0
07  75     +
08  33 2   RCL 2
09  45     ÷
10  01     1
11  34 5   SUM 5
12  33 5   RCL 5
13  75     +
14  33 3   RCL 3
15  45     ÷
16  01     1
17  34 5   SUM 5
18  33 5   RCL 5
19  75     +
20  33 4   RCL 4
21  45     ÷
22  01     1
23  34 5   SUM 5
24  33 5   RCL 5
25  85     =
26  13     ln
27  75     +
28  43     (
29  33 5   RCL 5
30  65     -
31  03     3
32  83     .
33  05     5
34  44     )
35  55     ×
36  43     (
37  33 5   RCL 5
38  75     +
39  83     .
40  08     8
41  05     5
42  44     )
43  32 5   STO 5
44  13     ln
45  65     -
46  33 5   RCL 5
47  85     =
48 -61     INV SBR