Apart from one significant difference it was exactly the same as its predecessor, the HP-25A. Even its codename "Squish" and its $200 price were similar to the codename "Squash" and the $195 price of the HP25A.

If the codename Squash suggested that a lot of features had been squashed into such a small package then the name Squish correctly implied that yet another feature had been squeezed in. This feature - the significant difference - was that the HP-25C was the first calculator with "Continuous Memory", as denoted by the letter C after its model number. This was very important - for the first time users could turn their handheld calculator off without losing the contents of its memory.

Naturally, as soon as you had this advantage you would want to write longer programs, since you would not have to retype them every time you turned on the calculator. The desire to store longer programs was dealt with in two ways - the use of cards instead of continuous memory, as already provided by the HP-65A and extended by the HP-67A and HP-97A - or the provision of more memory, as on the HP-25C successor, the HP-29C.

The HP-25C also introduced the idea of an upgrade to a model instead of its replacement by a different model - something we are familiar with nowadays, as in the case of the HP48 family.

This article is part of the WMJARTS file. This file contains a series of articles written by Wlodek Mier-Jedrzejowicz and published in DATAFILE, the journal of the HPCC. The article was reproduced with permission of the author.