\DeclareMathSizes {<t-size>} {<mt-size>} {<s-size>}
{<ss-size>}
Declares that <mt-size> is the (main) math text size, <s-size> is the `script' size and <ss-size> the `scriptscript' size to be used in math, when <t-size> is the current text size. For text sizes for which no such declaration is given the `script' and `scriptscript' size will be calculated and then fonts are loaded for the calculated sizes or the best approximation (this may result in a warning message).
Normally, <t-size> and <mt-size> will be identical; however, if, for example, PostScript text fonts are mixed with bit-map math fonts then you may not have available a <mt-size> for every <t-size>.
Example:
\DeclareMathSizes{13.82}{12.4}{10}{7}