This section is from the book "Building Construction", by R. Scott Burn. Also available from Amazon: Building Construction.

**Scales For Detail Or Enlarged Drawings**. These are constructed on the principle already explained for scales for general plans, but are designed to give facilities for measuring fractions of the inch, just as the division to the extreme left of scales, such as in fig. 6, Plate XXXVIlla., give fractions of the foot. And as there are eight equal parts in an inch, which are technically called " eighths of an inch," the last division of the scale to the left is divided into eight equal parts, each of which is equal to ⅛th of an inch as read off from the scale. A scale constructed on this principle is shown in fig. 14, Plate XXXVIIIa., which is a scale of 3 inches to the foot. The measurements are taken from this in the same way as already described, so far as feet and inches are concerned; but if, in the measurement, parts of an inch be given, the compasses are extended to the point indicating the measurement in the last division of the scale to the extreme left. Fig. 15 is a scale of |ths of a foot, or ⅝ths of full size. Detail drawings in practice, as a rule, are drawn to scales, some regular proportion of a foot, as ¼th of a foot, or " 3 inches to the foot," 1/6th or " 2 inches to the foot," and sometimes half size, which is equal to " 6 inches to the foot." The scales being named in the order above given, as " one-fourth full size," " one-sixth full size," " one-half size." When details are made, say half size, no regular scale is required to be constructed; as all the measurements can be taken from the ordinary foot rule, for all that is necessary is to take half of the full size measurements which the object would present: thus, if a distance was 6 inches, 3 inches would be taken; if 4 inches, 2 inches, and so on. Again, if the detail would be drawn to "one-fourth full size," one-fourth of the full size measurements would be taken: thus if the measurement was 8 inches, 2 inches would be laid down on the drawing; if 6 inches, 1½ inches would be taken from the ordinary foot rule, and so on. In these, the eighths of an inch, if any, in the measurement, would be approximately taken or allowed for: thus, ¾ths of an inch, or " six-eighths " in a detail drawing " half full size " would be represented by a measurement of three-eighths; an eighth by half this or "1/16th of an inch

Continue to: