[jdietrich]

I would strongly recommend adding a couple of dial indicator stands to your kit. They are rather more bulky than the included arms, but as they're designed for holding precise mechanical measurement instruments they are rigid, stable and can be very finely adjusted.

https://www.mcmaster.com/products/dial-indicator-stands/

For more complex probing, it is now remarkably straightforward to 3D print a bed-of-nails test jig.