The Smith chart. From W: " invented by Phillip H. Smith (1905–1987) is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency engineering to assist in solving problems with transmission lines and matching circuits."
Fallout Decay Nomogram - Used for calculating future radiation levels based on a known radiation level at a known time. Just draw a line through two knowns to find the third unknown. Timothy taught "nuclear math" and how to use nomograms for many years.