"To show the difference" means to present or display the contrast or variation between two or more things in order to highlight their distinctions or disparities. Full definition
The graph below of seasonal rainfall in mm shows the difference between the dark blue «winter as observed» and the dark green «winter in the world that might have been». (carbonbrief.org)
Initial results from first grade do not show differences in academic skills, but children who participated in preschool were less likely to be retained in kindergarten. (americanprogress.org)
Their sleeping pattern may be all over the place, but that doesn't mean you can't show them the difference between night and day. (thenaptimereviewer.com)