Agreed that a detailed discussion of blob radius is not appropriate here.
Maybe by explicitly naming the factor `sigma_to_radius` (see [here](https://gist.github.com/cdeil/11354543#file-plot_blob-py-L15)) and linking
to the API docs *which explain the returned `sigma` and relation to `radius`) in the text at the top most confusion by readers not familiar with these subtleties (like me) can be avoided.