Campaign map doesn't show the effect of experience, Battle map does. Battle map also shows the effect of fatigue, leader, etc on the unit. Best I can determine (looking at only basic Line Infantry), 1 chevron = +2 Accuracy, +2 Loading, +1 Melee, +1 Defense, +2 Morale. Can't promise that holds up all the way up as I've never gotten a unit above 3 chevrons. Also cam't promise that it is the same for other types of units (light infantry, arty, cav). What I listed is simply the difference noted on the Battle map for Line Infantry units from 2 seperate battles. Not an end all, simply a starting point.