To check the calibration on your Falcon MD 20 Metal Detector do the following;

1. Turn the Auto Gnd Bal knob fully to the left (fully counter-clockwise)
2. Set the copper ring on the BLACK line
3. Turn the MD20 on with the sensitivity switch (fully to the left but on)
4. Slide the copper ring toward the RED line

The MD20 should sound as the copper ring crosses the RED line. If it sounds off within a 1/16 inch either side of the RED line it is within calibration limits.