For making slight erasures, a very sharp knife skilfully used will be found effective, as it can be so manipulated as to affect nothing but the parts to be erased. Another expedient, where only a slight erasure is to be made, is to use a thin sheet of celluloid or durable cardboard, in which are cut small holes corresponding to the work to be changed. This sheet is laid on the drawing so that a hole comes over the part to be erased, then a sand-eraser is rubbed over the hole, and nothing is damaged except the portion which is changed.

FILING DRAWINGS, CALCULATIONS, SPECIFICATIONS, ETC.

In the course of a few years' practice the office records of a consulting engineer grow to such proportions that, unless some systematic method of filing and indexing them be adopted, it is impossible to refer thereto without a great deal of delay and annoyance. The filing of calculations and specifications is a comparatively easy matter, but to keep an accumulating lot of drawings in good shape for ready reference is by no means such. During the time that the author has been engaged in active practice several methods have been employed for filing tracings. One great difficulty with the earlier drawings was that they were of varying dimensions, some as large as forty-two inches by ninety-six inches, and others belonging to the same set as small as eighteen inches square. At first large cases of drawers were used for laying out the tracings flat, each tracing being stamped with numbers designating the lot and drawer to which it belonged, and an index being kept of all drawings recording the numbers of the lot and drawer. The objections to this method were that the smaller drawings got lost among the larger ones, thus often necessitating a complete overhauling of an entire drawer to find a tracing, and it was impossible to keep the large drawings from becoming folded and cracked at the edges and corners.

Later it was deemed advisable to bind each set of drawings together with patent fasteners along one end, but this method was soon abandoned, owing to the difficulty encountered in getting out tracings for blue-printing and reference.