Starting with hands, abacus and slide rule, humans have always reached for tools to simplify math. Pocket-sized calculators ushered in modern mathematics, helped build the atomic bomb, took us to the bottom of the ocean and accompanied us to the moon. The pocket calculator changed our world, until it was supplanted by more modern devices that, in a cruel twist of irony, it helped to create. The calculator is dead; long live the calculator. In this witty mathematic and social history, Keith Houston transports readers from the nascent economies of the ancient world to the First World War, where a Jewish engineer calculated for his life at Buchenwald, and into the technological arms race that led to the first affordable electronic pocket calculators. At every turn, Houston is a scholarly, affable guide to this global history of invention. Empire of the Sum will appeal to maths lovers, history buffs and anyone seeking to understand our trajectory to the computer age.