The zoom level is relative. Generally, you need to have it adjusted from the program you use. I'm not sure you can control it from Windows, as the programs do work independently. Using, say, various text programs, 100% isn't necessarily the same size for all programs.
The zoom level of your screen is also controlled through you video card controls. It's mainly an issue of resolution.
I know this isn't a proper answer. To get one, do give some info of programs in use. Screenshots of problem?