Replying to Got a Sachtler fluid head for $20 at a yard sale

So I scored this head for $20 having the feeling that it must be worth much more.

It says "sachtler - munchen" and has "P139" engraved on the side.

It didn't come with a plate and I am 99% sure its a 100mm ball.

It has 7 steps of tilt and 3 steps of drag. It also had a red dial that won't move and does nothing to my knowledge.

I am hoping one of you guys could give me some more info on this since I am not having the best luck googling around.