Ok... Now I need help in Calibration... PLEASE!!!

UconnL

So, I have a Whites MX6 and It has proved pretty good at the beach finding newer coins... Clad dimes, qtr's and halfs... Question???

It "boops" and shows qtrs in regualr dirt (soil), but when I dig down all I find are tin cans and can tops...

Suggestions to calibrate???

Thanks! Larry