Funny angles

Ya know, I can honestly say that I have never been in a house that has a wall at a perfect 90 degree angle!  Either the studs are out of plumb (even on new construction), the drywall is wavy, or something else is going on.  That being the case, a carpenter has to learn how to deal with it!
Here are some more pics of the fluted trim and corner block project.  In the movie room, there are some odd shaped walls.  Here's how I figured the angles:
First, I need to pick up the true angle to be trimmed.  I am fortunate enough to have been given a digital protractor by my late father-in-law - what a supreme piece of equipment this is - a real gem!  It instantly picks up the angle for me.  So: let's say that I find that the angle is 145 degrees. I deduct that from 180 degrees, leaving me 35 degrees. (I can also deduct from 90 or 270 to accommodate other angles of different degrees). Since we are making a mitered joint, we need to half that number, arriving at 17.5 degrees. This is what I will cut both miters at - 17.5. Using this simple formula will yield a tight joint almost always on the first try!  I use this method all the time, successfully. Click on a pic below for a closer view...