The units of measurement were micrograms per cubic meter. The mercury vapour analyser used detects mercury vapour. If mercury vapour is not present in a substance or in the environment it will measure zero. Mercury in food is a concern especially those who are very sensitive to it. I have found recently that when i avoid foods that have given off a high vapour reading my health is much better, and when i eat these foods its much worse. I suggest that anyone who is struggling to get on top of their health to give it a try and see if it makes a difference. I would be happy to talk to anyone more about it.