What does pc and em means?

Answer 1

'pc' is 'pica' a font size unit.
'em' is a special unit based on font height... so a margin of 1em represent a margin of same size as font.

Answer 2

http://www.w3schools.com/cssref/css_units.asp

Answer 3

as @Jani Sinkkonen said...
Generaly default font-size ( at least on desktop browsers, it more complicated on mobile devices ) is arround 16px, but in a hand you can have some inconsistences between browsers default values, and on the other hand you cannot be sure for future ^^

Answer 4

1em is relative to the elements font-size. If you define font-size to 20px in some parent element 1em equals to that.

Answer 5

1em = 16px

Answer 6

pc - pica

Answer 7

I am fairly certain 1em only equals 16px by browser default. em is the size of the text from the parent tag (if there is no size defined it would be default ) or the size of the letter m. This means that if you set the text to 10px and set a child tag to 4em it would be equivalent to 40px