The first sign of HP-35’s ln(2.02) bug

[Didier Lachieze]

I'm back home and have checked my Virtual Collection.

(09-10-2022 07:43 AM)EdS2 Wrote:  The archived site of the late Jacques Laporte says this:

Quote:In 1972 (probably by the fall of 1972) , when the problem was discovered, HP had sold some 25000 units, but only 5000 machines were returned to have their 3 ROM chips exchanged.

Bug free units were shipped starting January 1973 :
- Serial Number 1302AXXXXX (second week of 1973) and higher are error free,
- before that all units needed modifications.
The recall process started in February 1973: "We have taken immediate steps to correct the problem, and will have replacement read-only-memories available sometime after the first of the year" wrote Ron Stevenson Customer Service Manager, to the "Dear HP-35 Owner"

This is confirmed by appendix D of Remembering the HP 35A, in particular Fig. D4 & D5.

So assuming that all units prior to the date code 1302A were produced with the bug, this represents at least 77194 units (39071 1143A + 24776 1230A + 13347 1249A). This assumption is confirmed by the highest serial number with the bug in my virtual collection: 1249A 11780.

If, when the bug was discovered, there was 25000 units already produced*, this should have been in late August 1972.

I have in my Virtual collection 568 units with date code 1143A, 1230A or 1249A.
120 confirmed with the bug, 53 confirmed without the bug and 395 unknown.
So based on this small sample 69% of the units with a known status have the bug and 31% don't have it. This would indicate that a lot of the units recalled were not sent back to HP, 31% of 77194 represents 23930 units returned to HP.

Now for the Red Dot units, merging my database and the one from http://hp35.wz.cz/ (which I didn't so far to ensure that my collection methodology would be the same for Red Dot and non Red Dot units and to avoid an over-sampling of Red Dots) I come to these numbers:

• 113 units with a Red Dots serial number
• 95 units with the Red Dot on the front
• 52 Red Dot units with the bug
• 27 Red Dot units without the bug
• 16 Red Dot units with unknown status
  

*this 25000 number is floating around on the internet, but I’ve never seen any historical evidence from HP internal documents. So if someone can provide such evidence I would be more than interested.