HP-67 standard pac

[Wytnucls]

I just repaired the card reader on my HP-67.
It reads all cards of the standard pac correctly, except the one I used the most during initial reader troubleshooting. That card was rubbed with alcohol (Kontakt 60)a few times, to make sure no grit was introduced on the magnetic head. As anybody experienced a damaged card after cleaning it in this way before?

Also, each card of the pac is marked with a white bar pattern at top left. Was that just for quick identification in the field or does it serve another purpose?

[Jim Horn]

I noticed that when I bought mine in 1976. I suspect that was used to load the appropriate data onto each card at the factory. The bars are a simple BCD encoding of the card number (SD-01A through SD-15A in my set, with the bars representing 01 through 15). Considering the volume of calculators being sold back then, an automated way to be sure the right data was loaded would have been vital.

[Wytnucls]

Yes, that seems to be the logical explanation. I could not link the pattern to any known BCD code, but the pattern repeats itself from number 11 in a 6 bar pattern, instead of 4 bars.

[Jim Horn]

The encoding is simple: there's always a start bit (a small white square) followed every ~3mm by successive data bits of value 1, 2, 4, 8, 10 (and, assumingly, 20, 40, 80, 100, 200, 400, 800, etc.). A white square is a "1" bit; no square is a "0" bit.

There is room for 20 such bits, allowing values up to 99999. That should have been enough for all HP supported program cards! Even using the upper three digits for the card pack (I can't bring myself to drop the last "k" of that word), that's still 999 such program packs.