taking the speed, V, as 15 knots, the pitch of the propeller, P, as 27
ft. 6 in., and the revolutions per minute, R, as 60.
Set 27·5 on B to 10133 on A (N.B.—Take the setting near the _centre_
index of A); bring the cursor to 15 on B and 60 on B to cursor.
Reading the L.H. A scale backwards, the slip, S, = 8 per cent. is
found on A over 10 on B.
_Percentage Calculations._—To increase a quantity by _x_ per cent. we
multiply by 100 + _x_; to diminish a quantity by _x_ per cent. we
multiply by 100 − _x_. Hence, to add _x_ per cent., set 100 + _x_ on C
to 1 on D and read new values on D under original values on C. To deduct
_x_ per cent. read the D scale backwards from 10 and set R.H. index of C
to _x_ per cent. so read. Then read as before.