Font Size change?

["Richard Boaz" <riboaz xs4all nl>]

To all the font gurus:

In gtk+ version 2.6 I specified to draw some text on my drawing area using
the font "Sans bold 10" and received a favourable result.

In gtk+ version 2.10 I have not changed this specification and suddenly
the font is much larger than in version 2.6, to the point I have to change
it to make everything work as before.

I know this must relate to gtk+ since I have both versions installed on my
box and can simply point my application to one or the other and
demonstrate the difference.

I was under the impression that font sizes were fixed.  I guess I was
wrong.  But this confuses me, why would a font change real size across
different versions of gtk+?

On a more general note, how can I produce and provide my program across
multiple versions of gtk+ (now and into the future) without having to
worry about fonts changing their real size on the fly?

thanks for any pointers and explanations,

richard