Question

In CSS are you allowed to use .5 increments i.e

font-size: 8.5pt;

Can’t see the difference between font-size: 8pt and font-size: 8.5pt

Answer 1

Point values are really only for print CSS.

Quoting Chris C:

A point is a unit of measurement used for real-life ink-on-paper
typography. 72pts = one inch. One inch = one real-life inch
like-on-a-ruler. Not an inch on a screen, which is totally arbitrary
based on resolution.

Source: http://css-tricks.com/css-font-size/

The W3C Tips page suggest avoiding them for screen:

The so-called absolute units (cm, mm, in, pt and pc) mean the same in
CSS as everywhere else. A length expressed in any of these will appear
as exactly that size (within the precision of the hardware and
software). They are not recommended for use on screen, because screen
sizes vary so much. A big screen may be 60cm (24in), a small, portable
screen is maybe only 8cm. And you don’t look at them from the same
distance.

Source: http://www.w3.org/Style/Examples/007/units.en.html