Exemption for asbestos products requires manufacturers to maintain shift registers recording raw materials and output to verify fly ash content. Field formations must require manufacturers of asbestos cement products to maintain a daily shift register, using a prescribed proforma, recording each shift's raw material usage (asbestos, cement, fly ash, pulp), number of batches, total input and total finished output so that the percentage of fly ash in the finished product can be calculated from production records to verify eligibility for excise duty exemption.