I reckon these would be good settings for new users of the machine to start off with, a lot of newcomers to the GMP tend to spend a lot of time trying to suss "iffy" signals, it's best to start with to go for the good clean positive signals, this will get finds in your pouch and give you confidence in the machine, once you get the hang of it you can start to check the iffy's out with more confidence without wasting too much time
Setup for novice users
Coil 9" stock
Silencer: 1
Ground: 11 o’clock
Iron Volume: 11 o’clock
Iron Threshold: 15 Reduce as you gain experience with the machine (set to auto only if coke is a big problem)
Sensitivity: 11 to 1 o’clock
Setup for experienced users
Medium to heavy iron contamination
Coil: 9" stock (Far better than the 11" in iron, and sharper on the small stuff)
Silencer: 0
Ground: 10 o'clock
Iron Volume: 11 o'clock
Iron Threshold: Set on 6-6.5 (which is around the 10 o'clock mark, can be set just clicked out of auto, but you'll get far more "iffy" signals.)
Sensitivity: 11 to 2 o'clock (depending on ground and external interference, start at 11 o'clock, increase if poss to find optimum setting)
This setup works well with plenty of iron in the ground, you will dig the odd piece of iron, but the experienced user should be able to suss most of it out by the subtle tone difference that iron gives, also checking a target at a 90 degree angle will eliminate a lot of iron, the upside of this setup is you'll get very little "target masking", if your serious about getting small finds from amongst iron, never raise the iron threshold more than needed, if you set it in auto and leave it there your wasting the potential of this machine, as well as losing many finds that are masked by the iron, also when in auto you lose around a third of the recovery speed, and as some would say, the more discrim you use the more depth you lose.
It's important the silencer is on 0 as this gives the fastest recovery speed, this is vital if working amongst heavy iron contamination, if digging several pieces of larger iron, raise the iron threshold a small amount at a time until your happy with it, personaly i have never minded digging some iron, i'd much rather leave the iron threshold fairly low to be sure of getting those cut hammered, working in auto with the iron threshold will eliminate cut quarters and halves, if they are close to iron.
