.Anything to do with re-installing windows! There are always parts broken or missing, non scratched glass is tough to find, aligning them just sucks. Unless you do them all the time it is hard to remember how the regulators get installed and where all the parts go. Busted and scratched knuckles is the biggest issue...
The funny thing about science is that if you change one miniscule parameter you change the entire outcome to the way you want it.
