\begin{tikzpicture}
  \pgfmathparse{2} \let\R\pgfmathresult;
   %Sizing of canvas
  \pgfmathparse{\R} \let\FrameSize\pgfmathresult;
   %Number positions
  \pgfmathparse{0.925*\R} \let\NumPos\pgfmathresult;
   %Number positions
  \pgfmathparse{0.85*\R} \let\ArrowSize\pgfmathresult;
  
   \filldraw [white]
   (\FrameSize,\FrameSize)
   --
   (-\FrameSize,\FrameSize)
   --
   (-\FrameSize,-\FrameSize)
   --
   (\FrameSize,-\FrameSize)
   -- cycle;
  
   \coordinate (O) at (0,0);

   \filldraw (O) circle(1pt);
   \foreach \n in {1,...,12}
   {
       \pgfmathparse{\n*30} \let\Angle\pgfmathresult;
       \draw[-Latex,very thin,gray] (O) -- (\Angle:\ArrowSize);
       \draw (\Angle:\NumPos) node {\n};
   }

   \draw (O) circle(\R);
\end{tikzpicture}
