The one thing about the X-Terra 50's GB is that it is different from any detector I've used before. The XP Gold Maxx, from France, worked rather well in many sites I hunted with it, and it had a simple GB adjustment. You bobbed the coil and adjusted the knob until you just silenced the ground. This is similar to using a modified IDX Pro or Classic III in the Disc. mode, or Tesoro's Eldorado and other similar makes. If you have a too-negative GB you hear it when you bob the coil towards and away from the ground and if you adjust the GB while bobbing in the Disc. mode (aka Power Balancing as I've referred to it for years) you can get to the point where you're just positive enough for the Disc. mode to ignore ground signal.
With a conventional VLF, such as my Shadow X5, you try and balance in the All Metal mode for as close to perfect balance as you can and then make sure it is ample to be functional in the Disc. mode.
With many manually ground balanced models you will be able to sort of fine-tune them a little, depending upon the coarseness of the GB controlled circuitry. The X-Terra 50 is a bit different and the numeric-referenced GB 'segments' do not provide for 'fine tuning' the unit. With either X-Terra model it is very important to make sure you maintain a uniform coin-to-ground relationship on your side-to-side sweeps, especially as the mineralization level increases. And radical coil lift or bobbing, especially at higher sensitivity settings in 'bad ground' environments will produce some falsing.
Friday I hunted a site with the X-Terra 30 and had very little problem if I maintained oil position, even at a full sensitivity setting of '10'. This was mellower ground for around here and the X-Terra 50 balanced at about #5. The X-Terra 30's GB is factory preset at an equivalent #6
