@Eifelsucher : Danke Thomas für die Unterstützung

@Zeus:
Ich weiß schon von was ich rede, habe mich aber vielleicht falsch ausgedrückt, daher Auszug aus dem Tesoro LSt - handbuch:
"Take the quarter away from the searchcoil and wait several seconds. Notice the regular threshold sound returns—as the detector automatically retunes the threshold to its original level. Move the quarter close to the searchcoil momentarily and notice the loud continuous target response sound has returned also. Take the quarter away again. A detector operating in this way is called “All Metal Mode with Fast Auto Tune.”
Genau das war was ich meinte!