A simple “rotating wheel” calculator that, by matching the half-life and the elapsed time, allowed one to calculate the fraction of activity remaining in a radioactive sample. The 14 cm diameter calculator, made of paper card, was manufactured by AECL Commercial Products Division well before hand-held electronic calculators were available. The reverse side of the calculator listed the half-lives, in alphabetic order, of about 100 isotopes that might be encountered.
