Lincoln 2,218,388 to McClellan 1,812,807.
A difference of 405,581 votes. Or 10% of the total voting populas. Which could well have been the Army Vote. If you assume that the army voted very heavily for Lincoln instead their former commander George B. McClellan.
What is amazing to me is that in the case of David U. example of the Union Soldier who voted in a village somewhere between Hagerstown WV. and Winchester VA., How did that vote get counted when today we with all of our Technical resources cain't even count the ballots in our local districts correctly?