font familiy definitions - kindle conversions

[cybmole]

if an epub has specific font family definitions in its CSS on in its in-line code, what becomes of these in the conversion process ?

1. I assume that they have some initial value in that calibre viewer uses them for epub view.
2. are they then copied into the mobi file, as is, or dropped.
3. if they make it into the mobi file, does Kindle use them or substitute its own fonts ?

I have similar question for font sizing ( which can be small, medium , large, or can be 0.nnnn em style.
are these used & converted as is, and why do I often see strnge values with up to 6 paces of decimal precision in an initial calibre convert e.g. font size 0.7944... surely the human eye is not that! sensitive. so these things get rounded up / down for actual display use ?