A tachograph system comprises a sender unit mounted to the vehicle gearbox, the tachograph head and a recording medium. Tachograph heads are of either analogue or digital types. All relevant vehicles manufactured since 1 May 2006 must be fitted with digital tachograph heads. The recording medium for analogue heads are wax coated paper discs, and for digital heads are digital driver cards containing a microchip with flash memory. Digital driver cards store data as a .ddd file that can be imported into tachograph analysis software.