If you do hit the button in all metal non retune, you reset the tune by hold coil up in front of you and pressing retune button.
In disc, if you press button halfway by holding half thumb on the bezel around the button and half press, it's in non retune and push all the way retunes (acts same in half press as all metal no motion and fully pressed works like retune button in all metal no motion mode.)
In essen e, while staying in disc you can use it like the all metal no motion mode or like the fast auto retune all metal (pinpoint) without flipping switch
Until you understand the button it seems difficult to understand.
You can also use it like a pinpoint button in disc by just fully pressing it.
The auto mode you can use the switch for is a slow retune all metal.
I don't use all the abilities of the button but it is pressy cool what you can do with it all the while staying in disc mode.