Iron Settings

Metal detectors do not see Iron just as Iron. Big flat Iron will be identified as non-ferrous.
You have to test with Iron nails for correct discrimination.
Large flat iron is recognizable as Iron when the search coil approaches slowly from the side of the target. First the low tone/blue color will come followed by red color/high tone and in the end there will be again blue color/low tone. 

If Iron is indicated as non-ferrous, regardless of the coil in use, do the following discrimination adjustment:
This is the most effective method of setting the Discrimination level, for all search conditions.

• Pass a rusty iron nail (about 50 mm long) close to the search coil pointed against the coil center.
• While moving the nail left to right in front of the coil, adjust the Discrimination level from 0 by small increments until the Iron nail is indicated as Iron by Blue color and VCO tone will be low when the Iron nail is passing in front of the coil middle.
• With all coils Discrimination level 0 will be most receptive to all targets and higher levels than 0 less so.