## Parallelogram

Area equals base multiplied by height.

## Triangle

Base and height given. Multiply base by height and divide by two.

When three sides are given. From the half sum of the three sides subtract each side separately; multiply the half sum and the three remainders together. The area is the square root of the product thus obtained.

## Trapezium (A Figure With Two Sides Parallel And Two Sides Not Parallel)

To find the area multiply the sum of the two parallel sides by the distance between them and divide by two.

## Square Or Rhombus

(an oblique parallelogram with four equal sides). - Area equals half the product of the diagonals.

## Irregular Polygon

The area may be found by dividing it into a series of triangles and trapeziums, and finding the sum of the areas thus obtained.

## Regular Polygon

Area equals number of sides multiplied by length of one side and by the radius of the inscribed circle divided by two.

## Circle

Circumference equals diameter multiplied by 3.1416, or approximately by 3 1/7. Area equals diameter squared multiplied by .7854.

## Sector Of Circle

Multiply the length of the arc by the radius and divide by two.

## Segment Of Circle

Find the area of the sector having the same arc. Also find area of triangle formed by the radial sides and the chord. The area equals the sum or difference of these according as the segment is greater or less than a semicircle.

## Annulus

Multiply the sum of the diameters by their difference and by .7854.

## Square Equal To A Circle

Side of square equals diameter multiplied by .8862.

## Inscribed Square

Side of square equals diameter multiplied by .7071.

## Ellipse

Area equals the product of the two axes by .7854.

solids.

## Cube

Surface equals length of one edge squared and multiplied by six. Contents equals length of one edge cubed.

## Cylinders And Prisms

Surface equals perimeter of one end multiplied by height plus twice the area of one end. Contents equals area of base multiplied by height. This last also applies to oblique cylinders and prisms.

## Cone Or Pyramid

Surface equals circumference of base multiplied by slant height divided by two, plus the area of the base. Contents equals area of base multiplied by one-third perpendicular height. This last applies whether the cones and pyramids be right or oblique.

## Frustum Of Cone Or Pyramid

Contents : To the sum of the area of the two ends add the square root of their product and multiply the quantity thus obtained by one-third the perpendicular height.

## Sphere

Area equals square of diameter multiplied by 3.1416 or 3 1/7; i.e., it is equal to four times the area of one of its great circles, or to the convex surface of its circumscribing cylinder. Surfaces of spheres vary as the squares of their diameters. Contents equal the cube of the diameter multiplied by .5236, i.e., equals area of surface multiplied by diameter and divided by six. Contents of spheres vary as the cubes of the diameter.

## Segment Of Sphere

Contents: From three times the diameter of the sphere subtract twice the height of the segment, multiply the difference by the square of the height and by .5236; or, another rule: Add -the square of the height to three times the square of the radius of the base and multiply the sum by the height and by .5236.

## Zone Of Sphere

To the sum of the squares of the radii of the two ends add one-third the square of the height, multiply the sum by the height and by 1.5708.

## Cone, Sphere, And Cylinder

The contents of a cone, sphere, and cylinder of same diameter and height are in the ratio of 1 to 2 to 3. - Practical Engineer's Electrical Pocket Book and Diary.