hand calibrates usually means there is an additional process. A colorimeter is used but it can also be that a human worker oversees it, this is a setup beyond the initial calibration done at the factory and has some costs. For IPS panels there is also another process which is very manual and that is panel fitting, the panels are fitted by hand and tweaked a bit in terms of tensioning to reduce the amount of light bleeding that is native to IPS displays this is done to higher end desktop displays but I'm not sure if it can be done to a form fitted display like the one for the Surface.