Drawing ruler lines

Since you're using wxPython, you've given my a plumb

    > opportunity to repeat what is in danger of becoming my
    > litany:

    > You should check out Matt Newville's MPlot package and
    > my wxmpl module, both of which exist to simply embedding
    > matplotlib in wxPython applications. Both of them provide
    > user interaction bells and whistles, including crosshairs
    > around the mouse position.

Perhaps a wiki entry on using mpl with wx would be helpful.