24. Where the cost of an insured repair or fitting of a device or of one or a combination of components, adjustments or supplements is undetermined because no price has been entered on the list in the Tariff, the total cost assumed by the Board is determined as follows:(1) the rate fixed in the Tariff per quarter hour or fraction thereof for the time required for fitting or repair, or both, where applicable;
(2) the rate fixed in the Tariff per quarter hour or fraction thereof for the time required to make an adjustment; and
(3) the cost price of the materials is added to the cost arising from the application of paragraphs 1 and 2.