I would agree that the soldiers had a very good sense of distance traveled through their experience with constant marching, and from their earlier experiences on foot and horseback. The early explorers of 17th century Virginia's southwestern mountains measured distance through what woodsmen considered was a good day's travel from sunrise to sunset, which was about 40 miles a day on flatland. Soldiers of the 9th Alabama Regiment were amazingly accurate in their estimation of distances when they were camped in the Northern Virginia area.
Along with estimating distances, I have also wondered how soldiers were able to weigh themselves, as they occasionally reported their exact weight home in their letters. Anyone know or have any thoughts?