Knob with progress bar

A gain knob whose arc grows from the center position, to the left for cuts and to the right for boosts.

Drag, scroll or use the arrow keys. Double-click to reset to 0 dB.

How it's built

The ticks and the dark track share range-270 from-225, the usual knob sweep with the gap at the bottom. fit-range puts the first and last of the 25 .vectors on the two ends.
The colored arc is one <o-arc> without value, so it fills its ring's range. The script sets that ring's --o-from and --o-range: from the top for a boost, from the value back to the top for a cut.
The body is a satellite fifteen lanes wide on orbit-0. A satellite is a universe too, so the .gravity-spot inside it places the pointer relative to the knob, and rotate on that system turns it.
The universe is the role="slider", with pointer capture for dragging and the usual keys.