Thanks a lot too dop2000 :)
Unfortunately this is not the exact behavior I'm looking for.
If I'm not wrong, the side your knob is turning depend on the side I click on.
I'd like the knob to turn clockwise if I drag to the up, and anti clockwise if I drag to the down (regardless of where the user click), with a limit of around 300°, and it set a variable depending on the position.
The purpose is to make a knob smiliar to a gain/FX knob on a guitar amp.
I tried the newt's solution, but I only managed to do it to follow the mouse position, and the value is set to default at each click.
AS a workaround I was think about creating an invisible slider on the top of knob (because the behavior look a lot like of a fader one), but I have the same problem : beacuse the slider appears at the same place, the knob is not keeping his position so the value is set back to default each time I click on the knob.