Zachary Mathe

Secondary axes are used to conveniently display an alternative unit system. [Here are examples.](https://matplotlib.org/gallery/subplots_axes_and_figures/secondary_axis.html#sphx-glr-gallery-subplots-axes-and-figures-secondary-axis-py) mpldatacursor seems to not recognize secondary axes. If I do something like `ax2 = ax1.secondary_xaxis('top', functions=(fun1,...