Then the convex side is exposed and the board may straighten thus: Fig.

58.
By wrapping up small boards in paper or cloth in the intervals between work on them, they may be kept straight until they are assembled.
[Illustration: Fig.58.Clamping up Boards to Prevent Warping.] Another precaution to take is to be sure to plane both sides of a board if either is planed, especially if the board has been exposed to air-drying for some time.
WOOD MEASUREMENTS.
Lumber is a general term for all kinds of sawn wood.

Logs may be sawn into timber, that is, beams and joists, into planks, which are 2" to 4" thick, or into boards which are from 1/4" to 1-3/4" thick.

These may be resawn into special sizes.
Lumber is measured by the superficial foot, which is a board 1" thick, 12" wide, and 12" long, so that a board 1" thick, (or 7/8" dressed) 6" wide and 12' 0" long, measures 6' B.M.

(board measure).