What do these font-shape warnings mean?

Question

When I am compiling my document with pdflatex I get the following errors:

LaTeX Font Warning: Font shape `OT1/cmr/m/n' in size <5.5> not available
(Font)              size <5> substituted on input line 50.


LaTeX Font Warning: Font shape `OML/cmm/m/it' in size <5.5> not available
(Font)              size <5> substituted on input line 50.


LaTeX Font Warning: Font shape `OMS/cmsy/m/n' in size <5.5> not available
(Font)              size <5> substituted on input line 50.

What do these warnings exactly mean? The area where I think they are coming from is enclosed with {\fontsize{11}{12}\selectfont }. Also, the line number seems to be the place where a macro is called, and not the place in the macro where this is occuring.

How can I fix these warnings?

Answer 1

A size substituation of 0.5pt is harmless, but if you want to avoid it load the fix-cm package:

\RequirePackage{fix-cm}
\documentclass{article}


\begin{document}
\fontsize{11pt}{12pt}\selectfont $a^2$
\end{document}