Mackie Universal Control surface controller question...

[Rock]

Mackie Control Universal has four function vPots. I've only discovered three of the four ways in which Tracktion applies their function:

Track Panning
Plugin Control (filter control)
Aux Send Level

Does anyone know what the fourth function is assigned to control in Tracktion?

Thanks

[Rock]

Think I found it. Looks like it is marker.

[valley]

It is the marker. The ref manual covers this stuff, although it's a slog to read through.