On the vertical axis is instead reported the amount of pixels. The combination of these two data varies from photo to photo and there is enormous help in understanding the distribution of tones of the captured information.
It may happen that by mistake, technical limitations or artistic choice some parts of the histogram are found outside the histogram graph, below the value of 0 (black) or above that of white (255).
In fact, this type of phenomenon is to be avoided and at the limit managed in post-production where it is easier to visualize precisely which pixels we give up. The Graphic Photography Los Angeles procedure varies from model to model but usually just press the info button (or something similar) one or more times. Even from PC, smartphone or tablet you can view the histogram of a photo, but you will need one of the many software to edit photos (even the slightly more advanced viewers integrate it).