Marks

Placing a mark in the histogram can be usefull to know the actual data that its being shown by a concrete bar. Easily can be seen just by clicking on it, then a text label will appear with the value that the bar represents and the number of times this value has been repeated in the working volume.

Main Menu

Using main menu will provide you to reach to the options that you would like to 
see on your picture. Moreover the "Histogram Menu"helps you to see the 3 Axis volumed images with  "fill bars","match color" and "follow marks" submenus.
 

Section Browser

With the section browser you can browse your image in the small window which is shown your image in.