Page:Methods of Operating the Comptometer (1895).djvu/15



—In performing division or subtraction, both the black and the red figures are used to indicate the keys to be struck, and for convenience of explanation, the black figures will be named positive, and the red figures negative. The red figures are small and the black ones large.

When it is not specified whether the keys are positive or negative, it is to be understood that they are positive.

When striking the keys negative (according to the small figures), we always strike one less than the number itself, except that if there be ciphers on the right, deduct one from the nearest number to the right. Thus, in using the small figures, we would strike 83 for 84, 126 for 127, and 340 for 350, etc., etc. On the keys themselves the small figures are colored red and the large figures black, making the difference conspicuous.

When a number to be struck negative has a cipher or ciphers on the right, before deducting the 1, such ciphers must be disregarded in striking the keys, but when the ciphers occur between digits, they must be struck the same as the digits. Thus, in the number 1450, strike 1, 4 and 4 in the fourth, third and second series respectively, and pay no attention to the cipher in the units series. But should the number given be 1508, 1, 5, 0 and 7 must be struck on the keys.

It will be observed that there are no keys having the figure 9 in red. Wherever the figure 9 occurs in the number remaining after deducting the one, it is to be disregarded in striking the keys according to the red figures. Thus, to strike 5963, the red 5 must be struck in the fourth column of keys, and as 9 stands in the third order, we do not strike any key in the third column, but strike six in the second column, and two in the first or unit column.

Should the right hand figure of a number to be struck negative be "1," the cipher remaining after deducting one must be struck: as, for example, if 1561 is to be struck negative, after deducting one, the number 1560 will remain, each figure of which must be struck, including the cipher.