The Operations of the Geometric and Military Compass

We will always have them from the lines of which we are now speaking, and one of these will be the line already divided directly upon the Instrument, which has its beginning at the center of the Instrument; and this, which is a fixed scale, will serve us to measure the sides of the proposed Plan. The other, which will be for drawing the new Plan, must be mobile, that is, it must be able to be increased and diminished at our discretion according to whether the new Plan must be larger or smaller. Such a mutable scale will be that which we will have transversally from the same lines by tightening or widening our Instrument. But for a clearer understanding of the manner of applying such lines to use, we will provide an example. Let there be proposed to us the Plan A B C D E, to which another similar one must be drawn, but upon the line F G, the

A geometric diagram depicts an irregular pentagon with vertices labeled A, B, C, D, and E. The vertex D is at the peak, C is to the upper left, B is at the lower left, A is at the lower right, and E is at the upper right. Parallel to and below the base side BA, there is a shorter line segment labeled with the letters G (below B) and F (below A). A letter H is placed to the left of the side BC.

which is homologous, that is, it corresponds to the line A B. Here it is manifest that it is necessary to make use of two scales, one to measure the lines of the Plan A B C D E, and the other with which the lines of the plan to be made are measured, and this must be