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The HP-21 was introduced with an "old style" serial number add-on tag of 1504, however, a little later, e.g. 1512, it had a "new style" stamped-in serial number.

A number of models were produced before and after this "switch" periode, e.g. HP-55, 65 and 80, therefore my question: Which models, in addition to the HP-21, were produced with both styles of serial numbers?

Also, I have an early-version HP-38C manufactured approximately 6 months later than my late-version HP-38C (i.e. the lightweight version with the crisp keys), both from Singapore - was this common for the 30-series?

I am sure you collectors out there with gigantic collections can check this out easily.

Bo Kristoffersen


I got a HP 21 which has a stamped in S/N (1505A), just a week after yours.

BTW I'm sure Sweden will win tonight !!!