If \numberwithin{equation}{section} is defined and ,
the equation environment is used with out first creating a section,
it will produce 0.x numbering. To revert the effect of \numberwithin, use
the following:
\usepackage{chngcntr}
\counterwithout{equation}{section}
The command
\counterwithin{equation}{section}
will do the opposite.This command applies to figure and table environments as well.
Make equation numbering changes with sections, chapters,
\numberwithin{equation}{section} %sets equation numbers <chapter>.<section>.<index>
\numberwithin{equation}{subsection} %sets equation numbers <chapter>.<section>.<subsection>.<index>
\numberwithin{equation}{subsubsection} %sets equation numbers <chapter>.<section>.<subsection>.<subsubsection>.<index>
