Mechanical drawing. Elementary and advanced (1910)
Reid, John S. (John Simpson), 1856- · New York, J. Wiley & sons; [etc, etc.] · leaf 23
Fig. 14. … Fig. 15. spreads the blades sufficiently apart to allow for thoroughcleaning and sharpening. The hinged blade is thereforeunnecessary. The pen should be held in a plane passingthrough the edge of the T-square at right angles to the planeof the paper, and making an angle with the plane of thepaper…
