All meters shall be tested before being placed in service and no meter shall be so placed that shall not have tested at least 98% accurate. A record of these tests shall be kept, and each meter in service shall be subject to a bi-annual test at which times such meter shall be thoroughly cleaned, inspected, and repaired before being placed in service. In case any meter should be questioned as to accuracy by the customer, that meter shall be given a special test. Should such meter not prove to be 98% accurate, then adjustment of the amount shall be made dating from the previous settlement and credit given for the amount over-registered.
('83 Code, § 4-2 I.I.)