When the data does not form a 'perfect' parabola, Brent's minimization algorithm can't work so it will return the focus for the minumum measured FWHM and a warning that this does not guarantees the best focus.
This pull request fixes 2 alerts when merging c68096c598264173cff67739c5a845770de59e0a into 8fbd2aa64294346a741fb0264e396a2318285dbf - view on LGTM.com
When the data does not form a 'perfect' parabola, Brent's minimization algorithm can't work so it will return the focus for the minumum measured FWHM and a warning that this does not guarantees the best focus.