This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
You may procure 2 drawing-boards, 42 in. long and 30 in. wide, to receive "double elephant" paper. Have the boards plain, without cleets, or ingenious devices for fastening the paper; they should be made from thoroughly seasoned wood, at least 1 1/4 in. thick, as if thinner they will not be heavy enough to resist the thrust of the T-squares. The qualities a good drawing-board should possess are, an equal surface, which should be slightly rounded from the edges to the centre, in order that the drawing-paper when stretched upon it may present a solid surface; and that the edges should be perfectly straight, and at right angles to each other. With 2 boards, one may be used for sketching and drawing details, which, if done on the same sheet with elevations, dirties the paper, and is apt to lower the standard of the finished drawing by what may be called bad association. Details and sketches, when made on a separate sheet, should be to a larger scale than elevations. By changing from one scale to another, the mind is schooled in proportion, and the conception of sizes and dimensions is more apt to follow the finished work to which the drawings relate.