Digital tachograph machine’s record the amount of driving time performed in a given day and sends the data to a monitoring service station. Many trucks come with a built in digital tachograph machine. In order to properly use the digital tachograph, you must know how to use the tachograph card that goes with the equipment. In most states and countries there is a legal limit for how long a truck driver can stay on the road in one given day. This is designed to help prevent exhausted drivers from speeding down the highway.