Driving licence exam

Interchange number (F27)
”The sign indicates the number of the interchange. The sign may be supplemented with the exit road's designation. No other colour may be used.”

Interchange number is the same as exit road number.

Example of practical use: You need to call 112 because of an accident. You know you are driving on E20, but not much more. However, if you see the interchange number, the emergency vehicles get a more exact position and can thus arrive on the scene quicker.