(a) All meter test-standards shall be of types approved by this commission in accordance with Part 227 of this Title or, if not required to be approved in accordance with Part 227, whose accuracy is traceable to the National Institute of Standards and Technology. Certification will be conducted by this commission, by its designee, or by commission approved procedures conducted with standards or equipment that trace their accuracy to the National Institute of Standards and Technology.

1. (1) Bell provers shall be certified initially and at least once every two years.
2. (2) Transfer provers shall be certified initially and at least once every two years. This certification requirement may be extended to once every five years provided that an annual comparison test between the transfer prover meter and a non-working reference standard agree to within ± 0.25 percent proof at no less than 16 points between 10 and 120 percent of the rated capacity of the transfer prover.
3. (3) Sonic nozzle provers shall be certified initially and at least once every two years. This certification requirement may be extended to once every five years provided that an annual comparison test between the sonic nozzle prover and a nonworking reference standard agree to within ± 0.25 percent proof of the most recently certified sonic nozzle calibration proof.
4. (4) A non-working reference standard meter shall be certified initially and at least once every five years. Its accuracy should be established at no less than 16 points between 10 and 120 percent of its rated capacity.
5. (5) Temperature and pressure test-standards shall be certified initially and at least once every five years.

6. (6) Auxiliary equipment. Any type of auxiliary equipment connected to a test-standard shall be installed and tested in accordance with manufacturers' instructions or in a manner acceptable to the commission or its designee.

   (c) Additional meter test-standard requirements.

7. (1) The capacity of the meter test-standard shall meet the open rate test requirements of the meter being tested.
8. (2) Each certified meter test-standard shall be provided with a certificate bearing the serial number, date of certification, correction factor(s) and test limitations, if any.
9. (3) Each meter test-standard shall be recertified after being damaged, repaired, adjusted or disassembled where such could in any way affect its previous accuracy calibration. Also, each bell prover shall be recertified if moved.
10. (4) Only meter test-standards with an error of less than ± 0.25 percent shall be used without applying a correction factor.
11. (5) Each bell prover shall be adjusted to a static pressure in the order of 1.5 inches of water column above or below atmospheric pressure.
12. (6) Each transfer prover or sonic nozzle test-standard shall be adjusted to the same pressure and temperature or corrected for any pressure and temperature difference between it and the meter under test.
13. (7) Each meter test-standard shall be tested for connection-fitting tightness prior to its use.
14. (8) A nonvolatile sealing medium meeting the applicable specifications of the American National Standards Institute (ANSI) standard set forth in section 227.1(c) of this Title shall be used in all bell provers.

(b) Test-standard certification frequency.