I did them on my IDXPro 7 years ago. There a SAT resistor, sensitivity resistor, ID pod resistor, something else...basically makes it more sensitive and sparky, running it at wide open sensitivity like you could with a stock unit isn’t AS possible now, which is good....you’re now getting ALL of the possible performance out of it. The ID pod resistor is for accuracy/stability, the SAT resistor lets the threshold reset slower so as to not cancel out deep small stuff as easily. There’s also the part you install GB and TH pots on the case so you can adjust these at will, which is CRITICAL. Keith and Sven can tell you more, Mr. Bill initially came up with this mod to run in saltwater (I heard). It is HIGHLY recommended that these mods be done to make an already excellent machine into one that’s even more versatile with even more performance. You need to know how to run a stock one before these mods are done to get the most out of it though, so you know the difference and have experience with it. That would be my suggestion anyway...