The scales used for obtaining measurements on drawings are made in several forms, the most convenient being the flat, with beveled edges, and the triangular. The scale is usually graduated for a distance of 12 inches. The triangular scale, Fig. 30, has six surfaces for different graduations, and the scales are arranged so that the drawings may be made in any proportion to the actual size. For mechanical work, the common divisions are multiples of two; thus drawings are made full size, 1/2 size, 1/4, 1/8, 1/16, 1/32,1/64, etc. If a drawing is 1/4 size, 3 inches equals 1 foot, hence 3 inches is divided into 12 equal parts and each division represents one inch. If the smallest division on a scale represents 1/16 inch, the scale is said to read to 1/16 inch.
Fig. 30. Triangular Scale.
Scales are often divided into 1/10,1/26,1/30,1/40, etc., for architects and civil engineers, and for measuring indicator cards.