Tacho head unit calibration

No, the vehicle should not be used if the unit is out of calibration. A warning message would have been coming up every time a card had been removed for the last month and the operator’s forward planning chart should also have prevented this happening.

I don’t know why the warning is only shown when the card is removed, but they are all the same.

Yes a driver should refuse to drive to vehicle if the tacho is out of calibration, as they would be committing a offence by doing so.