Operations of the Geometric and Military Compass

we will always have from the lines of which we are now speaking. One of these will be the line already directly divided upon the Instrument, which has its beginning at the center of the Instrument; this is a stable scale that 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 capable of being increased and decreased at our discretion according to whether the new Plan is to be larger or smaller. Such a mutable scale will be that which we obtain from the same lines by transversally tightening or widening our Instrument. But for a clearer understanding of how to apply such lines to use, we will provide an example. Let a Plan A B C D E be proposed, to which another similar one must be drawn, but upon the line F G,

A geometric diagram depicts an irregular pentagon with vertices labeled A, B, C, D, and E. Below the side A B is a shorter parallel line segment labeled G F. A separate vertical segment labeled H is placed near vertex C. The diagram serves as a mathematical figure for a scaling operation explained in the text.

which is homologous corresponding, that is, corresponding to the line A B. Here it is manifest that one must use two scales: one to measure the lines of the Plan A B C D E, and the other with which to measure the lines of the plan to be made. This one must be