(a) Unless tests are made as provided for under subdivision (c) of this section, each company shall install a recording calorimeter at each of its testing stations required by subdivisions (a) through (d) of section 229.50 of this Part, the installation of said recording calorimeter to be subject to acceptance by this commission. Each recording calorimeter shall be maintained and operated by each company in such a manner as to continuously record the heating value of all distributed gas. Each recording calorimeter shall be calibrated weekly with a certified standard gas with a heating value that was determined by comparison with that of a standard methane, accurate to within 1.0 British thermal unit per cubic foot, certified by the National Bureau of Standards.
(b) The results of the calibration shall be recorded. Each said recording calorimeter shall be adjusted if it is determined to be in error.
(c) Other methods of determining heating value of distributed gas may be used providing they have been approved by this commission before they are used.