If you have recalibrated your tool and it is still jumpy, there is a good chance that it is time to replace your red foam backup pad. You can do this yourself with the 2.5mm Allen (hex head) wrench that came with your sanding kit. Simply remove the 4 machine screws that hold on your pad and replace with a new one, being sure to firmly tighten down the screws. You should tighten them all down to where they start to firm up and then move from screw to screw and tighten them down hard as opposed to tightening each one individually as you go. Much in the same matter as when changing a tire if you have ever done so.
Video for reference: https://www.youtube.com/watch?v=azbKpsCohfU&t=278s
