M2 Radiation Calculator (Front) Given the exposure rate (rads/hr) at a given time after a nuclear detonation the calculator can be used to predicts the exposure rate at any other time. It can also estimate the radiation exposure of personnel who are in the area at some time after the explosion.
This instrument is in fact two instruments, and is one of the earliest known examples of Oughtred's invention, published in 1632. Oughtred's circles of proportions was invented to facilitate the use of logarithms. Instead of using Gunter's lines with a pair of dividers, this instrument, by simply moving the two rules, could make a multiplication or division more effectively. One still required printed tables of logarithms to convert numerals into logarithms, and vice versa.