[texhax] Question on fontdimen

[Michael Barr]

Can someone tell me what is happening here?  The fragment

\newdimen\axis
\axis=\fontdimen22\textfont2

gives an error message:

! Font \nullfont has only 7 fontdimen parameters.
l.3 \axis=\fontdimen22\textfont2

If I modify it as follows:

\makeatletter
\check at mathfonts
\makeatother
\newdimen\axis
\axis=\fontdimen22\textfont2

it works as expected.  I do not even recall where I got \check at mathfonts 
from.

Michael Barr