Measure out 10 feet, from the center of your housing to the inside edge of the locator. Test at multiple distances to ensure a good calibration. If incorrect, bring your head to a clean environment and recalibrate.
Check jobsite for active interference
A source of active interference is anything that is emitting a signal that could potentially interfere with your locator. With the transmitter off, first walk the bore path in your first band selection, then walk back with the other band selected. Any spikes in signal strength are a sign of interference that could skew readings
Check jobsite for passive interference
Passive interference is any sort of object that distorts the signal from your transmitter before it reached the locator. A common source of passive interference is rebar reinforced concrete. Passive Interference can distort the signal from your transmitter and skew readings.