\renewcommand{\runitdivisions}{2}
\setlength{\unitlength}{0.75cm}
\renewcommand{\gridcolor}{magenta}
\referencesystem(0,0)(1,-1)(0.5,0.5)
\begin{center}
\begin{Picture}(-3.5,-3.5)(3.5,3.5)
\polargrid{3.5}{12}
\end{Picture}
\end{center}
