I have a eqinox 600,where i live is a 1700s site.been detecting it for 20 years with a number of high end machines,also buddies of mine detecting it,year before last pulled out 13 large cents with my atpro.just a little side note atpro not used in pro mode is useless,in pro mode its awesome totally different machine. but back to why im posting,everything im detecting is mostly in the teens,strong signal ,rotate around the target, still a strong signal,dig rusty nail.everytime.i have iron bias at 3. most targets are going to be below 13 inches that is where my atpro massed out.so my question is why the teen vdi numbers for iron and is there a way to get past the 13 inch mark. sidenote, the house I live was George washingtons surgeon during the revolutionary war. any help is greatly appreciated.