Hi Dave, sorry for the tardy reply. The following is something I put together some time ago. I think you may find it helpful.
Disc
With very few exceptions I leave this at the lowest possible setting, the very first notch. A new user, however, may benefit by making some adjustments, at least until he is fairly acquainted with the GT's tonal range on various targets. If working your typical park, moving the dial to about the 11:00 notch will help in rejecting the pesky pieces of foil littering many parks while still picking up most gold rings. I don't recommend increasing the discrimination past this setting though unless the user is just cherry picking a site. Keep in mind too that increasing the discrimination tends to have a negative impact on depth.
Notch
While this setting can be useful in some situations I personally never use it. The setting is intended to cancel out targets falling within a specific range. For example, when working a sports field littered with similarly sized pulltabs a user can set the machine to reject that specific target range while still picking up targets of a lower or higher tonal range. I personally prefer to use the tones as a means of discrimination, but that's just a personal preference. Experiment with this setting. You may find it to be useful at some sites.
Volume
I set this one to just about the 3:00 position. I have found that a higher setting tends to produce an echo on shallower targets which I find annoying. It differs with each user though, so experiment with it.
Middle switch top = all metal - on -off- Iron Mask
Leave it on Iron Mask ON. All metal is just that - it picks up all targets, even iron. You can switch to All Metal when pinpointing a target in PinPoint Mode or when working the beach.
Threshold/Silent
I have used the silent setting on some occasions, and it is helpful, but I prefer the reassuring slight hum of a well-set threshold. I would leave it at the threshold setting until you become comfortable with the machine. If you do decide to use the silent mode, first make sure you have a low and consistently smooth threshold before switching over to silent. If your threshold is barely audible or erratic when setting the machine to silent it can have a negative impact on the machine's ability to pick up deep targets.
Sensitivity
A properly set sensitivity and discrimination makes the GT a great coinshooting and relic machine. This setting is one you will need to pay close attention to since it is the one you will be using the most. In general, setting it at the 12:00 position will work well at most sites. Note that the more clockwise setting actually lowers the sensitivity, so a 2:00 position would produce a lower sensitivity than the 12:00 position.
To set the threshold and properly ground balance using this setting start with the 12:00 position. Make sure that there are no metal objects in the ground. Repeatedly lower and raise the coil from the ground, making sure the coil isn't at an angle. The threshold may initially change, but then it should hold steady. If it doesn't, decrease the sensitivity, moving it to about the 1:00 position. Once it holds, sweep the coil on the ground several times. This will allow the machine to read the ground's mineral content and adjust itself for it. You're now set to go! You can now increase the sensitivity though be mindful of any falsing.
Right top switch up = Track Middle = fix down = P/Point
Leave this setting on Track. Track and Fix are only active during All Metal mode and will have no effect while in discrimination mode. Pin Point mode is used in combination with all metal to pinpoint a target.
Noise Cancel
This can be useful in certain circumstances, as when there's another detectorist nearby and his machine is interfering with yours, or at areas where EMI tends to be a problem.
I hope that helps, Dave.
