7. The Menus / 7.3 Functions in the View Menu

7.3.18 Mark Extreme Values

If the menu entry Mark Extreme Values is turned on, all black and white areas on-screen will be marked. If this option is active, the title bar of document will show "Ex".

By using Options/Display/Extreme Values (see chapter 7.10.1.25) you can define, how the areas will be marked and which tolerance will be used for marking.