Update 5/23/2023:  I added 2 more models of the tray, both with notches, as I found it sometimes difficult to remove the calipers from the tray.  The standard notch is shown, and works well enough, but I also added a larger notch variant to give more room for a thumb (untested, but a minor change).

I remixed the original to be a tray, but also modified it to have a place for the thumbwheel that my set of calipers has, as well as a place to hold a mechanical pencil.  

As I do my cad work, I always need my calipers handy, and also a mechanical pencil.  The modeled pencil was for a GraphGear 1000 Drafting Pencil. 

I included the remixed step file, but only the tray contains the extra features.