Nct and Doe failures on emissions

This is a brainbee gas analyser,used for checking the emissions on cars and vans.Its importent to know when going for your nct or d.o.e.This is done by ourselfs on pre d.o.e or Nct check overs.Did you know that a hole in your echaust or leak can throw one of theses readings off whitch ends up in a fail.