Jointa calculates the tilt and rotation required for your crosscut saw.
You can now cut perfect ceiling cove mitres, for any given corner angle, with the coving material laying flat in your crosscut saw.

Enter the corner angle of your walls into the app, and hit calculate.
You now have tilt and rotation angles ti set-up your crosscut saw.
You can now lay the coving material flat in the saw for cutting.

Leads to extremely accurate joints to the internal and external corners of your coving job.