From Ross-Tech Wiki

4.5 What is the purpose of the "OBD-II" button? Why would I want to press it?
See the Online Demo/Manual for more information. You can use this test to determine whether a car is ISO/OBD-II compatible, i.e. whether it "speaks" the OBD-II protocols, if the car uses the ISO-9141 hardware layer for OBD-II. This has nothing to do with the VAG protocol that VW uses, and the results of this test have nothing to do with VAG-COM working with any VW/Audi/SEAT/Skoda vehicle. No VW or Audi products prior to model year 1996 are OBD-II compliant! Please note that most vehicles sold outside of the US are NOT OBD-II compatible, and even some US-market TDI's are not OBD-II compatible.