I think you're misunderstanding what the switch is. When you move the power switch on and off, it also moves a plate underneath the ST/XT markings so that you can't twiddle the ST/XT setting while it's on. The actual ST/XT switch is manipulated via a slide underneath that panel that can be moved by putting something tiny, like a straight pin, into that tiny hole and moving it. The tiny hole itself is the indicator of the current setting.