Two sets of ticks on a colorbar?


I am making some contour plots and in my field for this particular value, there are two widely used units. As such, it is very useful to have both units listed on the colorbar. To clarify: the colorbar’s normal ticks would be facing to the right and labeled with Unit Type 1, which was the units that the data were in when they were plotted. Unit Type 2 is simply a factor of X different than unit type two. It would be nice if I could add a second set of ticks to the color bar using a different locator and have them face left. Is this possible? Is there another way to display two values for each tick such that the colorbar shows both units?