A tachograph is a device that is put in vehicles such as lorries and coaches in order to record information such as how fast the vehicle goes, how far it travels, and the number of breaks the driver takes.
[British]
tachograph in British English
(ˈtækəˌɡrɑːf, -ˌɡræf)
noun
a tachometer that produces a graphical record (tachogram) of its readings, esp a device for recording the speed of and distance covered by a heavy goods vehicle