The Golden Mask 1+ DT (Dual Tone) metal detector is a fixed ground-balance machine working at high frequency of 18kHz. The detector is a special redesigned version of the original Golden Mask 1+, with added dual-tone sound (DT) - ferrous metals are indicated with a low frequency sound, while de non-ferrous objects are indicated with a higher frequency sound. With the DT sound, you hear the iron signals, but you always know if the target is good or not. In fact, the Golden Mask 1+DT is a new version of the 1+ UK model, but working at 18kHz and this makes it more suitable for gold prospecting. The GM 1+ DT is designed for use on normal to moderately mineralized soils. The machine has very simple controls, making it ideal for beginner users. With its high working frequency of 18kHz, GM1+ DT is very sensitive to small objects and low conductors as gold. The signal-processing engine is lighting-fast, so the machine performs great in trashy areas, separating iron from good targets (coins), even if they are very closely positioned. If you are asking why they still produce the one-tone version, here is the answer: the one-tone version goes a little-bit deeper on light soils, not too much, but there is some tiny difference.