(1) If upon test of displacement meters upon complaint (except as herein provided for meters tested in place), it be found that the weighted average percentage of accuracy of the meter, determined as hereinafter specified, exceeds 100 percent, the bills of the consumer shall be adjusted to the extent of such excess for one-half of the quantity registered since the last test unless it can be shown that the error is due to an accident or other cause, the approximate date of which can be determined, in which case it shall be figured back to such date; or unless the consumer has suffered no damage from said error by virtue of the fact that the meter has registered a quantity of water less than that allowed for the minimum rate of the applicable rate schedule.

(2) For the purpose of adjustment of consumers' bills, the weighted average percentage of accuracy of a displacement meter, except as herein provided for meters tested in place, shall be determined by giving a weight of two to the percentage at the rate at which the percentage of accuracy is a maximum and a weight of unity to each of the percentages at approximately the low and high rates of flow within “normal test flow limits”.