You can't have the best depth by running both you get more depth running a single freq or weighted to one side of what your looking for . If all the high tones are gone why look for them . It would be better to run a higher freq where everybody has ran a lower freq . Coins that are masked well respond better to a higher freq . subeI think this is one reason why they came out with multi frequency. Instead of trying to figure out which frequency is best for a particular target in a particular area and potentially missing others why not let the machine run both high and low frequencies simultaneously and seeing more of everything