% Basic TikZ-example, showing how to draw some circles

\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}