Testeur de compression

A compression tester is used to measure the compression pressure in an engine cylinder while the engine is at normal operating temperature. During use, all sparkplugs should be removed, and the accelerator kept pressed to the floor.

The tester is screwed or pressed into an empty sparkplug socket, and its dial - usually calibrated in 5lb steps up to 200-300psi - registers the pressure in that cylinder as the engine is turned over. Testers usually have an adaptor for different sparkplug sizes, and some have a release button for resetting the dial.