<code latex>
\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\usepackage{tikz}
\PreviewEnvironment{tikzpicture}
\begin{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%	
\begin{tikzpicture}
	\draw (0,0) circle (1);
	\draw [fill=lightgray] (0,0) circle (0.75);
	\draw [fill=gray] (0,0) circle (0.5);
	%\draw [fill=darkgray] (0,0) circle (0.25);
	%\draw [ultra thick,red] (0,0) circle (0.025);
	\draw [red,thick,->] (0,0)  -- (1,0)		node at (1,0)	[black,right] {1};
	\draw [red,thick,->] (0,0)  -- (0,0.75)	node at (0,1)	[black,above] {0.75};
	%\draw [red,thick,->] (0,0)  -- (-0.5,0)	node at (-1,0)	[black,left] {0.5};
	%\draw [red,thick,->] (0,0)  -- (0,-0.25)	node at (0,-1)	[black,below] {0.25};
\end{tikzpicture}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%	
\end{document}
</code>