frame gives great accuracy in inclinations of members, which is the all-important point in graphical computations, and the small load-diagram confines the graphics to a reasonable space. If the inclinations are correct, accurate results will be obtained with a very small load-diagram. The author's limits of error for graphical work are one quarter of one per cent at midspan and one per cent at the far end of span. Should the error exceed these limits, the graphical work has to be done anew. Smooth paper, sharp pencils, true triangles, and perfect straight-edges are necessary to secure good results, to which list should be added painstaking accuracy in every manipulation of the appliances.

All calculations on the standard sheets are made in black copying-ink; and when they are checked by another computer, as is the invariable custom in the author's office, all checkmarks and corrections are made in red ink, and each page checked is so marked and initialed by the checking computer, who not only verifies all the numerical calculations, but also follows carefully each step in the design so as to guard against all possible errors. The work of checking is greatly facilitated, if all the steps taken are indicated plainly, so that they can be easily followed by the checker. Each result checked is ticked off with red ink.

MAKING DRAWINGS.

Owing to the necessity for having several copies made of each drawing, the latter is first laid out in pencil on brown paper, and is copied in ink on tracing-cloth. In some simple designs, however, the pencilling is done directly on the tracing-cloth; but this is the exception rather than the rule. For convenience in handling and filing, it is very desirable to have all drawings made of a uniform size. After several years of experience, a size of twenty-nine inches in width and thirty-eight inches in length has been adopted as best suited for bridge plans. This size may be used for all detail drawings and stress-diagrams, but it is often necessary to increase the  length  for  profiles  and  general  drawings.   The  drawing  is  al-ways   made   on   the   rough   side   of   the   tracing—cloth,   as   it   is