There was a thread last year (?) about potential errors in gas pumps. The
short of it was that the standards were pretty tight, although they varied
by state. Anyway, one of the newspaper articles a link pointed to indicated
the procedure in the case of a question about accuracy was to take the pump
out of service within 24 hours until it could be scheduled for retest. Dunno
what state that was.
Typical out-of-tolerance results reported were around 1%, although one was