Upon record kept pursuant to Section 12-21-2090 and upon such other information as may be obtained the Commission shall calculate the number or amount of soft drinks that are ordinarily manufactured, mixed or compounded from such ingredients in accordance with the standard or average formula used therefor by bottlers, mixers and compounders of soft drinks and the result thus obtained shall be prima facie evidence of the sale thereof. But nothing contained in this section shall be construed to prevent any bottler, mixer or compounder of soft drinks from showing that he has actually not sold the whole or any part of the amount of soft drinks as determined by the above method of calculation. And the Commission shall, in making the above provided calculation, allow as a deduction the reasonable average loss for waste and breakage.