But you won't know if it's accurate, or at least as accurate as it should be, because it hasn't run its self calibration test at start up. This could be your licence that you are playing with. Worse still it could be your livelihood. The judge will have no sympathy when he sends you down as he'll know that it's specified you should get the instruments checked out if they don't perform the self test described in the manufacturers documentation. Bang to rights squire.