What is the “approximate effect“?
Due to his or her knowledge of technology and traffic law, the expert is able to certify certain components an approximate effect through inspection.
Two simple examples:
American brake lights emit red light like European brake lights do. Thus, they have about the same effect. They don’t need to be modified, despite the fact that the law demands a vehicle to be equipped with type checked (with EU/ECE-label) brake lights.
The glass does not comply with EU-regulations, but has "DOT" printed on it. Thus, it complies with US-standards which is sufficient for the officially acknowledged TÜV SÜD expert to certify an approximate effect.
For which components exactly is the expert allowed to certify an approximate effect?
There is a list under Imported vehicles guideline.