Fisher TH Pro oldie-unique

[bedrock bubba]

I bought a Fisher TH Pro model back in 76-77.
Its quite unusual, as it does a double beep for gold only!
And a single beep for other metals.

Years ago I talked to Fisher Labs, and they wanted to buy it from me, as the gold double beep thing was so unique.

Anyone know about it?
I have used it, and what I don't like, is you have to reset the gain and threshhold very often. But it does find even small gold if its near the surface. It does go ape-shiit over black sands! It is a VLF type, with 6" coil.