Chronograph. 19th Century artwork of an electromagnetic chronograph. Chronographs are used to record measurements over time. A stylus (at left) traces recordings on to recording paper (centre left). Cogs (centre and right) ensure a steady rotaion of the recording paper. Illustration from 'Memoire sur un projet de chronographe electro-magnetique et son emploi dans les experiences de l'artillerie' (Memoire on a draft electromagnetic chronograph and its use in artillery experiments, 1849) by Jean Baptiste Martin de Brettes.