ronniecruisin if your are looking for 'limited' disc with the Tdi Pro, you would do well to go to the White's Metal Detector website and look for the Tdi Field Guide. Not the manual but the Field Guide, it covers different settings etc. There is a video using a Tdi SL, made by White's; demonstrating discrimination techniques online. The basic information is out there. If on the beach or hunting in low mineral areas then I'll have a go at limiting iron targets.
When prospecting I do not disc, the heavy mineralization and the higher ground balance required are one reason. Another is that gold comes in various shaped and sizes, different purity etc, I dig every signal without exception. If its junk then I dig it and go again, maybe it was masking something good?
If looking for small gold then I might run in LOW, with a slightly positive ground balance, giving me improved small gold performance at the cost of large gold performance. It is quiet and hot on the small stuff, matched with the smaller Sadie 8 x 6 or something similar.
Some folks for example may use a DD coil with the Tdi. Friend of mine used a Platypus DD, not my cup of tea, much prefer a mono or folded mono myself. Seems to work better for me.
At the end of the day the Tdi Pro does offer limited disc on iron, by VLF standards it is limited, but under the right conditions it can work reasonably well. That Field Guide and video are food for thought.
All the best,
Karelian