Slide Calculator – an Abacus in disguise

A slide calculator is a type of small, hand-held mechanical calculator, primarily for adding and subtracting. The example shown opposite features parallel toothed metal strips within a metal envelope and a side-mounted stylus to operate it.

The Addiator-Gesellschaft company, based in Berlin, Germany, was a prominent manufacturer, and the term “Addiator” is often used as a generic term for this type of calculator.

First a clearing bar is raised upwards to set the calculator to zero. Then using the stylus in the relevant numbered slots, the number 4261 is entered to show on the result row.

On the abacus a bead above the bar represents the number 5, the beads below each have a value of one. Numbers are set to rest against the bar, so here we have 4,2, 5+1= 6, and 1 – the same as on calculator. The next step is to add ’92’.

The stylus is placed in the number 9 slot and the rule is that as it is in the red zone the pen is moved away from the answer window and around the bend to place to form the number 4351 – as also shown on the abacus on the right.

Now to add the ‘2’. The stylus is inserted in the hole opposite the ‘2’ in the first column and moved towards the answer window to form the final result ‘4353’.

The appropriate abacus beads are moved against the bar to show the same result.

Unlike most modern electronic calculators, no intermediary calculation results are stored by either the abacus or the pocket calculator.

The slide calculator was devised by Architect and Doctor Claude Perrault around 1670 based on the way an abacus operates. He called his invention ‘Abaque Rhabdologique‘ – Abaque meaning abacus and Rhabdologique meaning Rabdology, the practice of performing arithmetic using Napier’s bones. There is no evidence of a working copy being produced, however the concept later spawned various commercial versions as noted below.