The ground creates noise which the detector needs to filter out. The more minerals the more noise, which affects the stability of the displayed ID. Most newer detectors are a slow swing 2 filter design, whereas many of the older were 4 filter fast swing design. Those 4 filter detectors tended to be less noisy and more stable in ID than the newer 2 filter types and were favored for areas with more difficult ground. There is the Stability mode on the X-Terras(70,705) that allows them to mimic in a fashion the older 4 filters.
However the Tone ID & Visual ID then become un-ganged. Therefore to improve the Visual ID the Tone ID may not always match the Visual ID.
But, it's another example of the flexibility of the X-Terra's as the premier mid-range detectors.
From the manual:
Target ID Stability
The X-Terra 705 has a fine Discrimination Scale, but this may result in some instability of the
displayed Target ID in some areas with highly mineralised soil. In these cases, the Target ID numbers may be further stabilised by using the Target ID Stabiliser. The Target Tone may not always
match the stabilised Target ID. Activating Target ID Stability In the detection screen, press and hold
Mode for three seconds. The + icon will appear, indicating that Target ID Stability is activated.
To de-activate Target ID Stability, press and hold Mode for three seconds. The icon will disappear, indicating that Target ID Stability is de-activated.
HH
BarnacleBill