At close focus, there is a bar sliding below the screen showing you which part of what you see won't be in the nagative (above the bar) and what compensation you should apply to the exposure (there are some figures engraved on the screen. There are the coefficients to apply to the exposure given by your meter).
To use it, don't forget the select the lens mounted on the camera (55, 65, 80,...) , the selector being on the left side of the body (concentric to the Lock/Unlock button used for lens change).
The system is not that accurate by it is far better than nothing.