Create cove molding and get the right measurements?

[CorCas]

After a bit of trial and error, I've now figured out how to cut left and right inside corners on a crown molding. I'm using the method where I hold the molding as it will sit on the ceiling and then make the cuts.

But now to a perhaps silly question, how do I ensure a perfect measurement? For the left inside corner, the sharper end is downward, which is the measurement I want. How do I then cut to meet this marking? With the molding as it sits in the ceiling on the miter saw, how do I transfer the measurement to where the saw first meets the molding so that it results in the correct measurement on the long point?

 

[Thomas_Blekinge]

The theoretical answer: The difference between where the saw first hits the trim and the long point is the same as the trim's width.
The practical answer: I usually cut the trim a few centimeters too long. Then you can hold it where it should be and see that all angles etc. are correct and then fine-cut it with the same angle setting until it fits.