Methods of Using the Comptometer.
Do not try too complicated examples, such as interest, exchange, square root, etc., until thoroughly familiar with handling the keys in the operations of subtraction, multiplication and division.
Always depress each key as far as it will go, and never depress two keys at the same time, but allow one to come back to its place before another is depressed.
To set the machine at naught, depress the lever on the right of the machine with the third finger of the right hand and turn the knob from the operator a little. Then release the lever, and continue to turn until the machine stops.
Explanation of the key-board. It will be observed that there are two figures on each key, one a large black one and the other a small red one. The black ones indicate the keys to be struck in addition and multiplication, and the red ones, those to be struck in division and subtraction.
In speaking of the keys, those running in a line up and down are called a column, and those running in a line from left to right are called a row. Thus all the keys having a large 4 on top stand in a row and are called the row of 4s.
In explaining the key-board for addition and multiplication, the keys are called by the black figures on their tops. Beginning at the right of the machine, the first column running from 1 to 9 represents units; the second column, tens; the third, hundreds; the fourth, thousands, etc. Thus the 7 key in the fifth column indicates 70000, and the 3 key in the second column indicates 30; therefore, to strike 467 on the machine, depress the 4 key in the third column, the 6 key in the second column, and the 7 key in the first or units column; 467 will then be indicated on the register of the machine. This number being left on the register and some other being struck as, for example, 3261, the register will show the sum of the two numbers; in this case, 3728.
Addition.
Many users of the Comptometer, after several months' practice, become so familiar with the key-board that they do do not look at the keys at all when adding. Therefore we
