From the Minelab Equinox Owner's Manual page 52: Iron Bias (Advanced Setting) The Iron Bias setting adjusts the likelihood of the detector to identify a target as iron if it presents both ferrous and non-ferrous signals. All ferrous targets produce a combination of a ferrous and nonferrous response. Large ferrous targets can even present a stronger non-ferrous response. Also, a ferrous target adjacent to a nonferrous target can produce a similar response. The Iron Bias Settin