Resizing topographical maps?

I have a USGS 1:24,000 scale map (saved in PDF) that I would like to resize to a 1:25,000 so that it can be used with military protractors. Will resizing the map affect the accuracy? Does anyone have experience with this? Mathematically it should be reduced to 96%, but when I simply hold the protractor up to my monitor (viewed as full size) it appears to require reduction to 91%. Any advice on this matter?