Page:Methods of Operating the Comptometer (1895).djvu/27



Multiply the feet of each factor by the inches of the other, leaving the products to accumulate on the register. Multiply mentally the inches of one factor by the inches of the other factor, divide by twelve and strike the result on the machine as in addition. Divide the amount now on the register by twelve, leaving the quotient and the remainder on the register; multiply the feet of one factor by the feet of the other factor, over the quotient, when the number of inches will be indicated in the first two columns on the right of the register and the feet in the columns to the left.

It is obvious that in the mental calculation of the inches by inches, there will sometimes be a slight remainder which will be lost. This can be avoided by calculating it on the machine, instead of mentally, before multiplying feet by inches, and carrying all the operations three places further to the left.

37 ft. 5 in. multiplied by 19 ft. 11 in.

Multiplying 19 by 5, 95 appears. Then multiplying 11 by 37, 502 appears. 5×11÷12,=4.6. Therefore, add 4, when 506 appears. Dividing this by 12, 42.02 appears. Multiplying 37 by 19 over the quotient, 745 sq. feet. 2 sq. in., stone measure, appears on the register as the answer.

If there are three factors containing feet and inches to be multiplied together to obtain cubic feet and inches, observe in which one the inches can be the most easily stated decimally, then multiply the other factors together as illustrated above, and then multiply the other by the product, by means of one of the methods given for multiplying where the multiplier stands on the register. Page 9.