To calculate area of triangle a, b, c, Fig. 183. Measure in inches * the length of the base, a, b. In this case it is 71 in. Then take the perpendicular height, c, d. In this case it is 2.8 in. The rule is to multiply the base by half the perpendicular height, and the product gives the area.

The cutting-area of a given pattern for a certain system may be obtained by marking out the pattern a number of times, and measuring the area thus enclosed.

The following example will illustrate the difference between the surface-area, and the cutting'-area of patterns: Surface-area of pattern as Fig. 165 = 90 sq. in. Cutting „ ,, „ 167 = 92 ,, „

Surface „ „ „ 168 = 107 „ „

Cutting „ ,,

(a) cut to system, „ 169 = 115 ,, ,,

(b) „ „ ,, 170 =128 „ „ Surface-area of pattern as ,, 175 =71 „ ,, Cutting „ „

(a) cut to system, ,, 176 = 81 „ „ (6) 175 = 84 „ „

By keeping careful records of the cutting results of a particular shaped pattern, an estimate of the cutting-area, may be obtained, and this used to give the comparative

* It is recommended for convenience and accuracy that a decimal scale be used.

Or half the base multiplied by the perpendicular height may be used.

% To get the area of the shapes thus enclosed, the following rules will be useful: The area of a rectangle, square, rhombus, or rhomboid, is found by obtaining the product of the length by the perpendicular height. The area of a circle equals half the product of the circumference by the radius, or the square of the radius multiplied by 3.14159. basis for costing, the value for qualities being arranged on a similar plan to that previously described.

Fig, 183.

Fig. 183.

The cost of the various sizes in a range may be easily ascertained, providing the standard or sample size be known.

A number of parts may be cut in cardboard of even texture and weighed, and the results compared with an equal number of parts cut in card from the sample pattern. It is useful to have a table prepared on such a plan to be acquainted with the extra cost entailed in cutting, say, 5 to 7 over 2 to 4's women's.