I dug a wheaty up last month.I remember getting down about 5" and finding a rusty nail.I thought it must have just been a false signal.I stuck the probe back in the hole and got a penny sound.About 2" directly under the nail was the wheaty.I once found a Barber dime lying on top of foot long strip of iron.It was on the bottom edge of the iron.I really think that where the coin is lying in relationship to the iron makes a difference.Seems that when its an inch or two below the iron,it will respond a better.Dave