_Note dial movements only; ignore those of the pointer._ _Each time 1 on dial agrees with or passes fixed index_, ADD _1 to the above difference of digits_. _Each time 1 on dial agrees with or passes pointer_, DEDUCT _1 from the above difference of digits_. Treat continued multiplication in the same way, counting the 1’s used as denominator digits as one less than the number of multiplied factors. EX.—(8·6 × 0·73 × 1·02)/(3·5 × 0·23) = 7·95 [7·95473+]. Set 8·6 to index and pointer to 3·5. Bring 0·73 to pointer (noting that 1 on the scale passes the index) and set pointer to 0·23. Set 1·02 to pointer (noting that 1 on the scale passes the pointer) and read under index 7·95. There are 1 + 0 + 1 = 2 numerator digits and 1 + 0 = 1 denominator digit; while 1 is to be added and 1 deducted as per rule. But as the latter cancel, the digits in the result will be 2 − 1 = 1. When moving the dial to the left will cause 1 on the dial to pass _both_ index and pointer (thus cancelling), the dial may be turned back to make the setting. It will be understood that when 1 is the _first_ numerator, and 1 on the dial is therefore set to the index, no digit addition will be made for this, as the actual operation of calculating has not been commenced. In the Stanley-Boucher calculator (Fig. 23) a small centre scale is added, on which a finger indicates automatically the number of digits to be added or deducted; the method of calculating, however, differs from the foregoing. To avoid turning back to 0 at the commencement of each calculation, a circle is ground on the glass face, so that a pencil mark can be made thereon to show the position of the finger when commencing a calculation. _To Find the Square of a Number._— Set the number, on one or other of the square root scales, to the index, and read the required square on the ordinary scale. _To Find the Square Root of a Number._—Set the number to the index, and if there is an _odd_ number of digits in the number, read the root on the inner circle; if an even number, on the second circle. _To Find the Cube of a Number._—Set 1 on the ordinary scale to the index, and the pointer (on the back dial) to the number on one of the three cube-root scales. Then under the pointer read the cube on the ordinary scale. _To Find the Cube Root of a Number._—Set 1 to index, and pointer to number. Then read the cube root under the pointer on one of the three inner circles on the back dial. If the number has 1, 4, 7, 10 or −2, −5, etc., digits, use the inner circle. 2, 5, 8, 11 or −1, −4, etc., „ „ second circle. 3, 6, 9, 12 or −0, −3, etc., „ „ third circle.