To find the power transmitted by toothed wheels, given the pitch diameter _d_ in inches, the number of revolutions per minute _n_, and the pitch _p_ in inches, by the rule, H.P. = (_n_ _d_ _p_^2)/(400). Set 400 on B to pitch in inches on D; set cursor to d on B, 1 on B to cursor, and over any number of revolutions n on B read power transmitted on A. EX.—Find the horse-power capable of being transmitted by a spur wheel 7 ft. in diameter, 3 in. pitch, and running at 90 revolutions per minute. Set 400 on B to 3 on D; bring cursor to 84 in. on B, 1 on B to cursor, and over 90 revolutions on B read 170, the horse-power transmitted, on A. SCREW-CUTTING. Given the number of threads per inch in the guide screw, to find the wheels to cut a screw of given pitch. Set threads per inch in guide screw on C, to the number of threads per inch to be cut on D. Then opposite any number of teeth in the wheel on the mandrel on C, is the number of teeth in the wheel to be placed on the guide screw on D. STRENGTH OF SHAFTING. Given the diameter _d_ of a steel shaft, and the number of revolutions per minute _n_, to find the horse-power from:— H.P. = _d_^3 × _n_ × 0·02. Set 1 on C to _d_ on D, and bring cursor to _d_ on B. Bring 50 on B to cursor, and over number of revolutions on B read H.P. on A. EX.—Find horse-power transmitted by a 3 in. steel shaft at 110 revolutions per minute. Set 1 on C to 3 on D, and bring cursor to 3 on B. Bring 50 on B to cursor, and over 110 on B read 59·4 horse-power on A. Given the horse-power to be transmitted and the number of revolutions of a steel shaft, to find the diameter. Set revolutions on B to horse-power on A, and bring cursor to 50 on B. Then move the slide until the same number is found on B under the cursor that is simultaneously found on D under the index of C. This number is the diameter required. To find the deflection _k_ in inches, of a round steel shaft of diameter _d_, under a uniformly distributed load in lb. _w_, and supported by bearings, the centres of which are _l_ feet apart (_k_ = (_w_ _l_^3)/(78,000_d_^4)). Modifying the form of this expression slightly, we proceed as follows:—Set _d_ on C to _l_ on D, and bring the cursor to the same number on B that is found on D under the index of C. Bring _d_ on B to cursor, cursor to _w_ on B, 78,800 on B to cursor, and read deflection on A over index of B. EX.—Find the deflection in inches of a round steel shaft 3½in. diameter, carrying a uniformly distributed load of 3200 lb., the distance apart of the centres of support being 9 ft. Set 3·5 on C to 9 on D, and read 2·57 on D, under the L.H. index of C. Set cursor to 2·57 on B, and bring 3·5 on B to cursor, cursor to 3200 on B, 78,000 on B to cursor, and over L.H. index of B read 0·199 in., the required deflection on A.