I can't tell any difference. Maybe a ft or two in hundred feet. I mainly use the line counters for repeat ability. If I put it out 40 feet and get bit then I know I can put others out same and expect to be in the zone. Main thing is to have the same amount of line on each reel as close as possible. I fill mine with cheap bulk 15 mono, then walk off 150 ft, cut it then splice in my braid. Zero counter and reel in 150 ft. Counter will be going backwards so reading should be 850. My full is about a 1/4 in below the normal full mark on spool. Also full dosnt have to be completely full. Your full can be half full as long as your using the same reels where in theory the counters will read the same. Just use a 6 in rule and fill them the same. YES before someone chastises me it will not be correct. But there again if they are all really close you have the repeat ability. Say 40 out is really 53 and you catch fish then all reels spooled this way should be within a couple of ft at the same 40.
Some will say they have to be exact and I would agree if we were fishing for deep water walley, trout, samon or salt water fish. But pulling for crappie 99% of the time we are pulling less than 150 ft.