Ellsworth M. Longfield

“ With point 1 as a center and a radius equal to the hypotenuse of triangle 1–A, an arc is drawn below line 1–2. This is intersected by an arc drawn from point 2 with a radius equal to the hypotenuse of triangle 2–A. The intersection locates the point A on the pattern. With point 2 as a center and a radius equal to the hypotenuse of triangle 2–B, an arc is drawn bearing away from point A. This arc is intersected by another drawn from point A, whose radius is equal to line AB of Fig. ”

“ The base lines are now drawn in, but before drawing them the draftsman must determine the order in which he intends to develop the pattern. It will simplify the study of triangulation if a standard method of development is adopted. Every line should be considered as running in but one direction ”

“ In heating and ventilation, square and rectangular pipes are changed to round pipes, and ventilators with round shafts are mounted on rectangular bases. Wherever the cross-section of a pipe is changed to another shape the transformation should be gradual in order to avoid excessive friction. ”