Model: HP 35
Type: Scientific calculator
Pictures: HP 35 (v2) HP 35 (v3) HP 35 (wrong label)
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.

The first one shown here is the second revision. The first revision had a power led next to the power slider, which was a bit odd because when the calculator is on, the display also lights up.

University of Salford tag The second one shown here (graciously donated by Richard Pilkington of the University of Salford) is the last revision of this calculator. The markings are now on the keys themselves. This calculator had a nice tag painted on, it had apparently been in use at the University of Salford’s Electrical Engineering’s department. I have removed the tag but took a photograph of it as a reminder. You can see that the calculator has been used a lot, or at least has been switched on and off a lot, by the wear on the silver decoration above the power slider. Spacer

HP 35 / 80 naming error? Something strange is going on with one of the HP 35’s in my collection, the third one shown here. 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. According to other sources on the net, such as the excellent site The Museum of HP Calculators (link valid 2024-01-13), the designation should have been "Hewlett • Packard" or "Hewlett • Packard 35" (like the other ones shown here). I find this very strange. Since the key placement of the HP 35 and the HP 80 are alike, one might wonder if this is a front swap, however that seems impossible because the HP 80’s keys on the fourth row are wider, same as the second HP 35 shown here, and there are no signs whatsoever of any tampering. The name tag itself does not look swappable either. If anyone can explain this strange fact, please send me an e-mail.

There’s some information on the HP 35 on HP’s official website (link valid 2024-01-13).

In 2007 HEWLETT PACKARD introduced the HP 35s, 35 years after the introduction of the HP-35, to celebrate the HP 35.

The HEWLETT PACKARD Company Archives site also has some information on this calculator, see Adding Innovation: The HP 35 (link valid 2024-01-13).

The website vintagecalculators.com (link valid 2024-01-13) 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 2024-01-13).

For more information on this beauty please refer to the better sources, like The Museum of HP Calculators (link valid 2024-01-13).


A power adapter.