Font Size

2 types of of measurements, absoulute and relative
Relative:
em
ex
px
%
Keywords

Absolute:
mm
cm
in
pt
Keywords

as a rule for screen design, we shouldnt use points to control our font size.
Resons are browser compatibility, and font sizes are fixed.
use points are only for print in css.
mm,cm,in, as a rule these should only be used to control our print sizes.
72pt = 1 inch