Operations of the Geometric and Military Compass

of the other, larger or smaller according to the proportion of the line F G to A B. Therefore, take the line A with a compass, and apply it directly upon the scale of the Instrument, placing one leg of the compass at the center of the Instrument and the other upon the point where it falls—let us say, for example, at 60. Then, take the line F G with the compass, and having placed one of its legs at the point 60, open the Instrument until the other leg falls exactly transversally upon the other corresponding point 60. This configuration of the Instrument will not be changed further, but all the other sides of the proposed Plan will be measured upon the straight scale, and the distances corresponding to them will be taken transversally for the sides of the new Plan immediately. For example, if we want to find the length of the line G H corresponding to B C, take the distance B C with the compass, apply this directly from the center of the Instrument upon the scale, and having fixed the other leg at the point where it falls—let us say, for example, 66—turn the other leg to the other point 66 corresponding transversally, according to whose measure you will cut the line G H, which will correspond to B C in the same proportion as the line F G to A B. And note that when one wishes to transfer a small plan into another much larger one, it will be necessary to use the two scales in the opposite order: that is, use the straight scale for the Plan to be made, and the transversal one to measure the lines of the proposed Plan, as, for example, if we have the Plan A B C D E F which we wish to transfer into another much larger one, that is, upon the line G H which is to correspond to the line A B, to adjust the scales take