Many slide rules have the sign (Prod.)/(−1) at the right-hand end of the D scale, while on the left is (Quot.)/(+1.) It is somewhat unfortunate that these signs refer to rules for determining the number of digits in products and quotients, which are used to a considerable extent on the Continent, and conflict with those used in this country. By the Continental method the number of digits in a product is equal to the sum of the digits in the two factors, if the result is obtained on the LEFT _of the first factor_; but if the result is found on the RIGHT of the first factor, it is equal to this sum − 1. The sign (Prod.)/(−1) the _right_-hand end of the D scale provides a visible reminder of this rule. Similarly for division:—The number of digits in a quotient is equal to the number of the digits in the dividend, minus those in the divisor, if the quotient appears on the RIGHT _of the dividend_, and to this difference + 1, if the quotient appears on the LEFT of the dividend. The sign (Quot.)/(+1) at the _left_-hand end of the D scale provides a visible reminder of this rule. The sign +ⵏ– ⟵ⵏ⟶ –ⵏ+ found at both ends of the A scale is of general application but of questionable utility. It is assumed to represent a fraction, the vertical line indicating the position of the decimal point. If the number 455 is to be dealt with in a multiplication on the lower scales, we may suppose the decimal point moved two places to the left, giving 4·55, a value which can be actually found on the scale. If we use this value, then to the number of digits in this result, as many must be added as the number of places (two in this case) by which the decimal point was moved. If the point is moved to the right, the number of places must be subtracted. Similarly, in division, if the decimal point in the divisor is moved _n_ places to the left, then _n_ places must be subtracted at the end of the operation; while if the point is moved through _n_ places to the right, then _n_ places must be added. The sign referred to, which, of course, applies to all scales, completely indicates these processes and is submitted as a reminder of the procedure to be followed by those using the method described. The signs π, _c_, _c′_, and M are explained in the Section on “Gauge Points,” p. 53. On some rules additional signs are found on the D scale. One, locating the value (180 × 60)/(π) = 3437·74 and hence giving the number of minutes in a radian, is marked ρ′. Another, representing the value (180 × 60 × 60)/(π) = 206265, and hence giving the number of seconds in a radian is marked ρ″. A third point, marked ρ_{˶}, placed at the value (200 × 100 × 100)/(π) = 636620, is used when the newer graduation of the circle is employed. These gauge points are useful when converting angles into circular measure, or _vice versa_, and also for determining the functions of small angles.