Weighbridge
The weighbridge is the scale in the pit lane where cars are called for a mandatory weight check during practice and qualifying.
A driver summoned to it must stop; ignoring the call is a penalty, and so is driving away under power once the car is on the scale — it has to be pushed off.
There is a minimum weight for car and driver together, and being under it is a disqualification. It is why drivers pick up marbles on the slowing-down lap and why fuel samples are taken at the same time.