Brand: Aristo
Model: M 42
Type: Calculator
Picture: Aristo M 42
Batteries: AA x 2
Lifetime: Introduced: 1977
Terminated: unknown
Notes: This calculator by Aristo is a beauty. It has a very solid case with a removable transparent lid. Take the lid off and this beauty of a calculator is revealed. The lid can conveniently be snapped on the back of the calculator. Small bumps on the lid should protect it from scratching.

It’s a plain calculator but with the non-standard option of swapping operands.

To indicate an error all decimal points light up. During normal operations the leftmost decimal point is used to indicate a non-zero value in memory.

There is no battery compartment visible at the back of this calculator. Instead there is a little notch at the bottom to enable lifting the calculator out of its back cover. There you can insert or replace the two AA batteries. Contrary to what one would expect, both batteries face the same way. Everything of this calculator seems to be designed with aesthetics in mind.

There is also storage for one spare AA battery. At frist I had no idea why, for one should always change all batteries when they are flat. That is until I found the Aristo M 85 S scientific calculator with the same form factor but is powered by three AA batteries!

A brief manual of the calculator’s functions is printed on the back.

The calculator accepts Alcaline batteries but also NiCd batteries. Aristo sold their own NiCd batteries under number Aristo 6773. The NiCd batteries can be charged using the Aristo 6773 battery charger.

According to an X-Number World article I once read (no longer linkable), the German brand Aristo only entered the calculator market in 1972 and left it due to heavy competition in 1978.


A power adapter (Aristo 6760).
A NiCd battery charger (Aristo 6773).