This year marks the 50th anniversary of the HP-35, the first pocket scientific calculator and HP’s first consumer product. For an excellent illustrated introduction, see
- The HP-35 at codex99
Over on the HP Museum forum Didier Lachieze presents some research on the production history, having collected and analysed some 1600 serial numbers:
An HP-35 Production Overview
The order rate was much higher than anticipated and the HP-35 went quickly on backorder. Six month after introduction it was estimated that the fiscal 1972 sales would be three times the initial expectations despite a 12-week delivery. See the HP Measure June 1972 article “A superstar is born”
Perhaps see also Testing chips for the HP-35 in ‘73