Model: HP 35
Type: Scientific calculator
Pictures: HP 35 HP 35
Batteries: Battery pack
Lifetime: Introduced: 1972
Terminated: 1975
Notes: HEWLETT PACKARD's first pocket calculator and the very first scientific pocket calculator. Apparently called the HP 35 because it has 35 keys.

In a time where other, often quite expensive, calculators could only do the standard four functions and sometimes a square root, HEWLETT PACKARD was able to proce this beautiful calculator. This calculator doesn't have the complex look of later HP calculators because there are only three keys with double functions, ARC SIN, ARC COS and ARC TAN.

Talking about those functions, there is only one angular mode available, DEGrees. Maybe an odd decision since PI is also available as a constant. Still, being able to produce a pocket calculator with these functions at all is a feat in 1972.

Very powerful for its time, uses RPN and includes useful scientific functions such as trigonometric functions and their inverses (using the "arc"-key), natural logarithms and powers (using the "x^y"-key).

As usual with the early HP calculators, this calculator as a very strong case and keys that simply won't wear out.

HP 35 / 80 naming error? Something strange is going on with the second HP 35 in my collection, the one shown on the right. When I found that one on a flea market I first thought I had found an HP 80, HP's second pocket calculator. On closer inspection however it turned out to be a HP 35 with a "Hewlett • Packard 80" designation on the front. According to other sources on the net, such as the excellent site The Museum of HP Calculators (link valid 2022-12-30), the designation should have been "Hewlett • Packard" or "Hewlett • Packard 35" (like the one on the left).
Also, the one on the left has all its markings on the keys themselves whilst the one marked 80 has them above the keys. If anyone can explain this trange fact, please send me a mail.
Very strange. Since the key placement of the HP 35 and the HP 80 are the same one might wonder if this is a front swap, however that seems unlikely because the key designations are on the front itself and there are no signs whatsoever of any tampering. The name tag itself does not look swappable.

There's some information on the HP 35 on HP's official website (link valid 2022-12-30).

The Hewlett-Packard Company Archives site also has some information on this calculator, see Adding Innovation: The HP 35 (link valid 2023-01-07).

The website vintagecalculators.com (link valid 2023-01-25) has a page with interesting information from the book "A Guide to HP Handheld Calculators and Computers," by Wlodek Mier-Jedrzejowicz. See this page (link valid 2023-01-25).

For more information on this beauty please refer to the better sources, like The Museum of HP Calculators (link valid 2022-12-30).


A power adapter.