How accurate are CSS's real-world units?

问题

I'm beginning experiments with CSS' real-world units, specifically, in and cm, for purposes of printing.

Are these units based on how they will be displayed on-screen or how they will be printed by a printer? How accurate are these units?

回答1:

According to W3C, only em, px and % are recommended for screen, the others for print.

Therefore, in a print application, the in and cm measurements could be precisely accurate.

There is an excellent article on such applications here:
http://meyerweb.com/eric/articles/webrev/200001.html

来源：https://stackoverflow.com/questions/7341808/how-accurate-are-csss-real-world-units