Like Mango says, the optimum frequency depends on what you are looking for and what your site conditions are like. Any machine at any frequency can find the easy targets. When you factor in target depth, soil conditions, target composition, target size, EMF, etc., using the right frequency for the conditions at hand can make all the difference. I've often had marginal signals on nice targets basically go away when I changed frequencies. The opposite is also true of course. If I only had one choice, for the majority of hunting I do, an 8kHz would be a general frequency that I could live with. I wouldn't be happy with it all the time though. It is nice to have multiple frequency options !