Note that under the cursor line we have the original number, 22·2, on A, and from this the number of digits in the root is determined as before. The plan of finding the square of a number by ordinary multiplication is often very convenient. The inverse process of finding a square root by trial division is not to be recommended. To obtain a close value of a root or to verify one found in the usual way, the author has, on occasion, adopted the following plan:—Set 1 (or 10) on B to the number on the A scale (L.H. or R.H. as the case may require), and bring the cursor to the number on D. If the root found is correct, the readings on C under the cursor and on D under the index of C, will be in exact agreement. If 1 on B is placed to a number _n_ on the L.H. A scale, the student will note that while root _n_ is read on D under 1 on C, the root of 10 _n_ is read on D under 10 on B. Hence, if preferred, the number can be taken always on the first scale of A and the root read under 1 or 10 on B, according to whether there is an odd or even number of digits in the number. Obviously the second root is the first multiplied by √(10). CUBES AND CUBE ROOTS. In raising a number to the third power, a combination of the preceding method and ordinary multiplication is employed. TO FIND THE CUBE OF A NUMBER.—_Set the_ L.H. _or_ R.H. _index of C to the number on D, and opposite the number_ ON THE LEFT-HAND _scale of B read the cube on the_ L.H. _or_ R.H. _scale of A_. By this rule four scales are brought into requisition. Of these, the D scale and the L.H. B scale are _always_ employed, and are to be read as of equal denomination. The values assigned to the L.H. and R.H. scales of A will be apparent from the following considerations. Commencing with the indices of C and D coinciding, and moving the slide to the right, it will be seen that, working in accordance with the above rule, the cubes of numbers from 1 to 2·154 (= ∛(10)) will be found on the first or L.H. scale of A. Moving the slide still farther to the right, we obtain _on the_ R.H. _A scale_ cubes of numbers from 2·154 to 4·641 (or ∛(10) to ∛(100)). Had we a _third_ repetition of the L.H. A scale, the L.H. index of C could be still further traversed to the right, and the cubes of numbers from 4·641 to 10 read off on this prolongation of A. But the same end can be attained by making use of the R.H. index of C, when, traversing the slide to the right as before, the cubes of numbers from 4·641 to 10 on D can be read off _on the_ L.H. _A scale_ over the corresponding numbers on the L.H. B scale. Hence, using the L.H. index of C, the readings on the L.H. A scale may be regarded comparatively as units, those on the R.H. A scale as tens; while for the hundreds we again make use of the L.H. A scale in conjunction with the _right-hand_ index of C.