The Addo X Series 20 is a calculator invented by the swedish company Addo AB.
The Addo calculator series includes different models, all of which provided both a purely mechanical and an electromechanical version.
Models differ from each other mainly for their capacity.
It must be noted that some machines with
lower capacities have been produced with the Model 21 frame, presumibly to recycle unused parts and to allow subsequent upgrades.
Another difference is in the naming of the calculators: the fullkeyboard models were named “Addo”, while calculators that had keyboards with just 10 keys were
named “Addo X”.
