**Hewlett Packard HP-35**

**Hewlett Packard HP-35**

**Distinctive features:** The first hand-held scientific calculator.

On April 14th 2009 Hewlett Packard was awarded the IEEE Milestone in Electrical Engineering and Computing for the HP-35 calculator for the first hand-held scientific calculator.

**Technical details:**Display is scientific, 10 digits mantissa and 2 digits exponent, red LED.

Scientific, using Reverse Polish Notation (RPN) - as evidenced by the lack of an "=" key.

Main integrated circuits in this example - Mostek *MK6020*, *MK6021*, *MK6022*, *MK6023*, *MK6024*, which comprise an arithmetic and
register chip, a control and timing chip, and three 256 x 10 bits ROMs. This chip set was also second-sourced by AMI (American Micro-systems Inc.).

3.75v (3 x AA re-chargeable).

79 mm x 147 mm x 34 mm (3.1" x 5.8" x 1.4").

Introduced February 1972, cost $395 (about £165 GBP).

Made in U.S.A. & Singapore.

The calculator illustrated is an early example since it has no model number on the front, just 'Hewlett●Packard', since this was the only hand-held calculator then marketed by Hewlett-Packard. Later examples are labelled with the model number—'Hewlett●Packard 35'.

The small ceramic package on the right is the *MK6020* Arithmetic & Register Chip, the large ceramic package on the left is the *MK6021* Control and Timing Chip, and the three cans in the middle are the *MK6022*, *MK6023*, and *MK6024*,
all 256 x 10 bits ROM chips. Here all chips are date-coded to late 1972.

The press release for the award of the IEEE Milestone in Electrical Engineering and Computing for the HP-35 calculator says *"Introduced in 1972, the HP-35 was the world's first handheld-sized scientific
calculator. An instant hit, the HP-35 ultimately made the slide rule, which had previously been used by generations of engineers and scientists, obsolete.*

*The HP-35, named for its 35 keys, was the first handheld calculator to perform transcendental functions such as trigonometric, logarithmic and exponential functions.*

*In the first three years after its introduction in 1972, sales of the HP-35 Scientific Calculator exceeded 300,000 units."*

This was the first hand-held scientific calculator. Previously, for their calculations, engineers and scientists would have used a slide-rule or a large desktop electronic scientific calculator. Now they could use a pocket-sized electronic calculator, if they could afford the price or persuade their company to provide
one. Hewlett Packard calculators were very well made, and reliable, and their electronics instruments have always had a very good reputation. Together with the high specification, this made their calculators the models
of choice for many professionals. In total, 300,000 *HP-35* calculators were sold^{[1]}.

The cost of the *HP-35* put it out of reach of many such as poor students, so other companies started to introduce scientific calculators with lower specifications and lower cost. While nearly all of the other calculator manufacturers concentrated on reducing the cost of their calculators, Hewlett-Packard largely maintained the cost and increased the functionality. They launched the *HP-65*, the first hand-held programmable calculator, in 1974, though they did introduce their own lower specification and cost scientific calculator in the *HP-21* in 1975. Hewlett-Packard are one of the few companies to continue making calculators from the early 1970s to the present day.

There is a lot of interesting information available about the *HP-35*, including:

- The article
*"The HP-35 Calculator: The first Electronic Slide Rule"*, in the Collecting Calculators section of this site, has further information about the*HP-35*.

- There is an enormous amount of information about the
*HP-35*gathered by David Hicks at the*Museum of HP Calculators*at http://www.hpmuseum.org/hp35.htm.

- There is a very interesting article
*"Made in the USA ... finally"*about the development of the HP-35 on Rick Furr's calculator site, available in the archive at https://web.archive.org/web/20040203113550/http://www.vcalc.net/hp-35.htm.

- An article on the development of the
*HP-35*, "The HP-35: Consumer Electronics, an Origin Story", at http://codex99.com/design/the-hp35.html

- An IEEE article
*"MOS CIRCUIT DEVELOPMENT FOR THE HP-35"*at http://www.hpmuseum.org/forum/thread-3745.html. - An article from the journal
*Electronics*:*"The HP-35: a tale of teamwork with vendors"*at http://www.hpmuseum.org/forum/thread-3746.html.

- There is a lengthy video on Youtube with an interview with Dave Cochran who was involved in the development of the
*HP-35*at https://www.youtube.com/watch?v=0IlSjfgrHVM.

- If you would like to try out the "Reverse Polish Notation" operation of a very realistic virtual
*HP-35*visit Neil Fraser's site at https://neil.fraser.name/software/hp-35/.

**Hewlett Packard awarded the "IEEE Milestone in Electrical Engineering and Computing" for the HP-35 calculator
**

On April 14th 2009 Hewlett Packard announced that it had been awarded the prestigious "IEEE Milestone in Electrical Engineering and Computing" for the HP-35 calculator, the first hand-held scientific calculator.

Left to right presenting the IEEE HP-35 Milestone Award are: Lewis Terman (IEEE), Dave Cochran (HP-35), Richard Gowen (IEEE).

The press release explains:

*"Introduced in 1972, the HP-35 was the world's first handheld-sized scientific calculator. An instant hit, the HP-35 ultimately made the slide rule, which had previously been used by generations of engineers and scientists,
obsolete.*

*The HP-35, named for its 35 keys, was the first handheld calculator to perform transcendental functions such as trigonometric, logarithmic and exponential functions.*

*In the first three years after its introduction in 1972, sales of the HP-35 Scientific Calculator exceeded 300,000 units.*

*An IEEE Milestone plaque recording the award will be permanently displayed at HP Labs in Palo Alto, Calif., the site where the HP-35 was originally developed."*

**July 2007: Hewlett Packard launches Retro HP 35s to Commemorate 35th Anniversary of First HP Handheld Calculator.** More information on the Vintage Calculator News page.

Photograph of HP35s used with permission of HP.

See also the Hewlett Packard *HP-80*, the first hand-held business and financial calculator, and the Hewlett Packard *HP-65*, the first hand-held programmable calculator.

**A Guide to HP Handheld Calculators and Computers**

Revised Guide to HP Calculators Available

The fifth edition of Wlodek Mier-Jedrzejowicz's "**A Guide to HP Handheld Calculators and Computers**" has been published.

**Hand-held Calculators**

*Vintage Calculators *

© Text & photographs copyright Nigel Tout 2000-2020 except where noted otherwise.