One workaround would be to remove the calculation from Azimuth_d & Azimuth_gr and have both of those fields as input fields. Then add two more rows (maybe, "Result: Azimuth in Degrees" & "Result: Azimuth in Gradients") and put your coalesce calculation there. I would also make these two results fields readonly.
If you implement this method, you could also clean this up a bit by starting with a select_one field, where the end user selects which type on conversion they would like, and only the appropriate fields show for that type of conversion (using the relevancy column).
Hope this helps!