Addo-X electric printing adding machine, model 154, by Addo Machine Co. Ltd., England

This 10-key motor-driven calculator was made in Addo’s English factory in Cirencester in the mid-1960s. It was used to train students in Secretarial Studies and Office Practice in colleges of Further and Higher Education. Unlike previous Addo models, it has a plastic rather than metal casing and separate function keys at the top left for positive or negative multiplication by repeated addition or subtraction.

Addo was a Swedish company based in Malmo that mainly manufactured calculators. It was established in 1918 by Hugo Agrell to produce full-keyboard adding and listing machines and from 1936 it introduced ten-key calculators, like this one, named ‘Addo-X’ with the X representing a Roman 10. The introduction of decimal currency in 1966 in Australia and 1971 in the UK grew their popularity. Addo merged with rival Swedish company Facit that produced typewriters in 1966 which was subsequently taken over by Electrolux in 1972.