tattletale
noun
1
in trucking, a device that records time and speed data, used by company officials to assure compliance with laws and regulations. Known conventionally as a 'tachograph' US, 1962.
2
in motor racing, a specially designed tachometer that measures and records the engine's highest speed during a run or lap US, 1965.
3
in trucking, a dangling chain that shows the approximate weight of the load by its distance from the axle US, 1961