Two straight-edges, each of equal width throughout, can be laid on edge, one across each end of the surface to be tested. Stand back a little and look across the top edge of one to the top edge of the other, and if these edges agree you may know at once that there is no winding where you have placed the straight-edges (Fig. 688). By putting them in different positions you can finally determine whether the whole surface is true or not.

Winding Sticks 716

FlG.688.

Winding Sticks 717

Fig. 689.

It is more accurate to use winding-sticks considerably longer than the width of the piece to be tested, as then any warping or winding will be exaggerated and more easily seen (Fig. 689). If the upper edges of the sticks are thin, or " feather-edged," it is easier to tell exactly when they are in line, but this does not ordinarily matter, except in work requiring extreme accuracy.

To find, for example, when the legs of a table, chair, or the like are cut so that the article will stand evenly, turn it over with the legs sticking up, put straight-edges on the ends of the legs, sight across these (Fig. 690), and trim one or two legs until the edges are in line. See Scribing for other methods. Warping or winding of short pieces can be detected by simply laying one straight-edge diagonally from corner to corner (Fig. 691). This will show at once which parts require to be planed to make the surface true.

Winding Sticks 718

Fig. 690.

Winding Sticks 719

Fig. 691.