Page:Methods of Operating the Comptometer (1895).djvu/14

 method will be found advantageous. In this rule we will call the number standing on the register of the machine the multiplier and the one not on the machine the multiplicand.

Observe the figure which stands in the highest order of the multiplier; place the finger on the key representing that figure and standing in the same column; strike it one time less than is indicated by the first figure on the right of the multiplicand; move one key to the left and strike it as many times as is indicated by the next figure of the multiplicand. Continue to strike each succeeding key to the left as many times as is indicated by the corresponding figure of the multiplicand. Observing the figures standing in the next highest order on the machine, proceed the same as with the first.

17+(4×30)+(360×2)×2,743. First add 17; then without turning the machine to naught, multiply 30 by 4, then 360 by 2, when the sum of all these operations, 857, will have accumulated on the register of the machine. The next step is to multiply 2,743 by 857, which stands on the register. As 8 stands in the highest order on the register, (third column), place the finger on the 8 key of that column and strike it two times, as two is one less than three which is the right hand figure of the number 2,743. Then move one key to the left and strike four times; moving one more key to the left, strike seven times, and again moving one column, strike two times. The next figure of the multiplier is 5 and stands in second column. Therefore, place the finger on the 5 key of that order and strike two times; move to the left one column and strike four times, etc. Proceed with the last figure of the multiplier, which is 7, the same as with the first two, when the answer, 2,350,751, will appear on the register.

it is desirable to reverse the system of striking the keys and work from the left to the right. By doing so, examples which would otherwise be too large for an eight column machine can be computed. Thus: 486.34286 X 75.8763. Begin on the highest key in the row of 7's and strike it four times; move one key to the right and strike eight times, etc. The answer expressed on the register will be 36901.8952 which is correct to the second decimal place.

It is obvious that when decimal fractions occur in any kind of computations, all that is necessary is to point off in the usual way.

Where high decimals are used and the keys are struck from the left, point off as many holes from the left as there are places to the left of the points in the multiplicand and multiplier. There is one hole to the left of the highest column of keys, therefore, with the product of 2.487634×3.24692 we would have 08.07+ and with the product of 8.76321×6.76342 we would have 59.26+.