It looks like the lower button is a GB button. I just figured being a multi freq machine it wouldn't have a GB feature like the Etrac? It seems that most machines that have GB adjustments are 1,2 or 3 freq machines. I wonder if the 3030 will give us a choice of running just one freq of our choice then the ability to manually GB? This seems like it may be better suited for low conductive targets being able to run say 18 kHz only?