A tachograph is a machine fitted inside a lorry, bus or coach that keeps a record of how the vehicle has been driven: how fast it went, how far it travelled, when it was moving and when it was stopped. Older ones drew lines on a round paper disc, one disc per day; newer ones are digital and store the record on a card that the driver puts in. Why it exists: it watches the driver's hours. A tired driver of a heavy lorry is dangerous, so the law in Europe and Britain limits how long a driver may drive before resting, and the tachograph is the proof. Police can stop a lorry and read it. If the record shows the driver drove nine hours without a break, there is a fine. So the word lives in the world of trucks, buses, transport companies and traffic law. It is a normal everyday word to lorry drivers — they shorten it to 'tacho' — but most other people never say it. It is much more common in British English than American, because the rules and the name came in through Europe. Note also that a tachograph is a specific piece of equipment, not a general word for a recorder.

行車紀錄器（大貨車、遊覽車上記錄車速、里程、駕駛時間的那種）。注意：台灣人講「行車紀錄器」多半是指拍影片的 dashcam，那是另一種東西；這個 tachograph 記的是速度和開車時數。