Stoneridge question?

Just started driving for a new firm, been given an old 08 scania everything seems to be ok but the tachograph keeps coming up saying “7/8 next calibration” anyone any idea what this means??

Damo_hall:
Just started driving for a new firm, been given an old 08 scania everything seems to be ok but the tachograph keeps coming up saying “7/8 next calibration” anyone any idea what this means??

GUESSING - it must be calibrated no later than the 7th August