Tachograph

A tachograph records what the vehicle and the driver did: time spent driving, time on other work, breaks, rest and speed. It applies to lorry and bus drivers under drivers’ hours rules, and the record it produces is what an enforcement officer inspects at the roadside.

Because the rules on hours are arithmetic rather than judgement — so many hours driving, a break of so many minutes, a daily rest of so many hours — they are among the most learnable marks on the lorry and bus paper, and among the least guessable if you have not learned them.

The driver is responsible for operating it correctly: selecting the right mode, keeping records available for inspection, and reporting a fault. A tachograph that is broken does not suspend the hours rules; it obliges you to keep a manual record instead.