Trial and error.
and it will never work properly because you have zero control over which fonts and sizes the client actually uses. You can define the sizes any way you want them, but the end-user can always override it.
Plus the sizes are interpreted differently on IE/Netscape/Opera/Mozilla.
I suggest you try PDF for printable docs, then you truely are in control.
A forum, a FAQ, email notification, what else do you need?