It probably should be noted that 0.5mm in 10mm is 5%

0.5mm is difficult to pick up with a ruler graduated in mm (our TE's aren't too sharp, surfaces aren't deep and the throws are small) so the worst case scenario of having one elevator traveling up 10.5mm and the other traveling up 9.5mm (a 10% difference in travel) is possible.

Converting the mm value to degrees allows me to use an expanded protractor scale arrangement where one or two clicks of subtrim are actually noticable. If I were setting the throws on an aileron that's 4 or 5 inches deep with ~45deg travel eack way, then being a millimeter or two out at the end of the travels isn't a big deal..

Getting the mechanical setup right is the best place to start before you start messing around with endpoints and whatnot...