Tangential line drawing instrument - consists of equilateral triangular prism with base line below ridge and transverse line

摘要

The instrument consists of an equilateral triangular prism, on whose base is a line running parallel to and directly beneath the ridge, also a line at right angles to this line. The latter line can be a side of the prism base, or of a rectangular baseplate joined to the base, and it can be pressed or engraved into base or baseplate, running centrally down it. The baseplate can be scaled, and a pair of holes can be provided in the cross line, equidistant from the base line on either side of it. Precision lines can be drawn in an easy way using the instrument.