Page 324 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 11: Artifact Drawing 303
to be extracted without disturbing the setting. The thickness is then obtained quite simply by subtracting the block thickness from the overall measurement.
B. DRAWING AIDS
Several different drawing boards are available varying in size and price. The simplest is the A3 clipboard in which the paper is held in position by a magnetic clamp. Vertical and horizontal grooves at the edge of the board give facility for a parallel rule arrangement. The rule slides up and down or across in these grooves. The rule has a groove too, so that another rule can run at right angles. There are rotating heads available which can be set at any given angle. It is a cheap and cheerful version of the drawing head on a proper drafting stand. These boards are very useful and convenient; the A3 size is about twice that of an illustration in a publication, so, as discussed above, drawings can be photographically reduced by one half to give a much better finished result.
Large-scale drawing stands are useful for a large office setup; they are expensive, but often essential. Some manufacturers now produce a cheap drawing machine that can be fitted on an ordinary drawing board, and this offers a compromise in size and money between the A3 board and the large drawing stand (Rotring A2 Portable Drafting Machine). These are really useful in field situations where large plans are needed, but where it is impos- sible to put a drawing stand. As the last resort, an old fashioned T-square,
Figure 11.5 Proportional dividers used to scale measurements. The dividers have the common proportional measurements set so that the proportionality ratio can be set.