How to put a big dot (and circle) over a variable?

Question

Example: Click here

where one can see a big dot (and circle) over W. I am using \dot{W} and \mathring{W} but seems not big enough.

Answer 1

\documentclass{article}
\usepackage{accents}
\begin{document}
$\accentset{\bullet}{b}$
\end{document}