First of all: This is not a three-way switch. To do that: just use
Button Groups.
This is different from using button groups in that each value continues to send out while the user continues up or down. This is a variation on the Relative Control (sends 127, 64 and 0, usually).
Set it up like this:
Note: Knob-etc = Knobs or sliders or crossfaders or XY pad dimensions
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Set a supercontrol Knob-etc. (or slider/crossfader)
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Make supercontrol of type (or subtype) relative
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Supercontrol options: supercontrol is sequential
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Give it three subcontrols (Knobs-etc.)
Set the supercontrol to have "sequential" subcontrols (options for super)
should switch between them.