My first comment regarding discrimination with a ground balancing PI like the TDI and others is that people may be expecting things of the TDI it cannot deliver, and may be better off with a good discriminating VLF detector. If your priority is discrimination, no PI will discriminate like a VLF. There are two ways to tune the TDI. The first and preferred option is to tune the detector for the best depth. On low mineral beaches ground balance "off" usually give the best performance and you g