In January 1972, Hewlett-Packard introduced the HP-35 "to give you a high precision portable electronic slide rule" as declared in the User Manual.

That meant a huge challenge at that time:

- the ability to perform a broad variety of computations as compared to the usual 4 operations : logarithmic, powers, direct and inverse trigonometric functions ...,

- a way to override the parenthesis scheme and to be able to store intermediate results in a calculation: the 4 register operational stack,

- the capacity to store if needed partial results for later use in a problem (a memory register),

- a 200 decade range to display values in a format similar to standard scientific notation, allowing numbers between 10-⁹⁹ to 9.999999999 10⁹⁹ to be manipulated. 

I will cover, in depth, the key inventions that HP brought to this project, without forgetting technological and economic context of this saga, as well as the portrait of the key men involved.

I will describe HP 35 hardware architecture and will comment the calculator firmware, detailing the key algorithms function by function: ln, log, sin, cos, 1/x .. etc, giving commented trace of sample run on a HP35 ROM simulator.

A way to pay tribute to this brilliant machine.

Photo credit :
1) HP-35 SN 1143A 34233, photo Jacques Laporte 2005,
2) "Some things are changing for the better", in Scientific American,May 1972, p.14, Agency "Richardson Seigle Rolfs & McCoy Inc.

© Hewlett-Packard Company 1972.