I designed and built this as a means to keep an eye on the state of my 3D Printer bed level.
To use it, once the bed has been set up and levelled in the usual way the 2-Axis level is placed on the bed and the X and Y screws are adjusted so that the bubbles are centered.

The screws are then locked down. If at any time you need to confirm that the bed has not altered simply place the level tester on the bed and observe the bubble. If it is in the center in each then the bed is the same as before.

In order to use it as a regular 2-Axis level, say for shelves, then it simply needs to be calibrated on a known level surface.

This was designed in Shapr3D, sliced in Cura and printed on Creality CR-19S Pro with white PLA filament.

Note, the holes are threaded for M4 screws, but in the one that I built I actually drilled them out to 5mm and pressed in threaded inserts. The small ball needs to be glued into the hemispheric hole on the arm to form the pivot. This was done in order to be able to print the arm flat on the bed without the need for support, which would have been required had the pivot dome been part of the model.

The spirit level bubbles are 39.75mm by 9.5mm and were bought on eBay for a couple of pounds each. They were glued in with epoxy when the level was on a flat surface before the pivot ball was glued in. This makes sure that they are inserted relatively horizontally. The ball is then glued into the socket and the screws, with lock nuts, are then screwed into the holes at the end of the arms.