Based on your red line on the board, that is NOT a 30 degree angle, most certainly an obtuse angle like 90 + 30 or 120 degrees.
See what I mean about the "confusion"? All because the settings are not the resultant angles on the workpiece, rather than "subtracted from 90 degrees". The "reference edge" in this example is against the face of the gauge. This concept is just common knowledge by framers and those who use a Speed square and miter saws.
With all due respect, take a few minutes and go to the shop, set your miter gauge to 30 and make a cut. Measure the cut angle with a protractor and see what you get. If you set the gauge to 0 and make a cut, the angle is 90 degrees to the edge of the board, so the settings are subtracted from 90 degrees! Your 45, 30, and 60 triangles from drafting are good visual examples to keep in mind.
Here's an excerpt from my post titled "Angles and settings on the Miter Saw":
If it weren't for my buddy coming over this AM I never would have thought about this, He's a rough carpenter/framer. I tell him about our discussion settings vs angles. He pulls out his speed square and goes " No problem, This is the same as the miter saw." I go HUH?? He goes "YAH, I always think away from 90 since 90 is plumb/vertical." I go HUH? What are all these other nos on this thing for? He goes "These are the angles if you pivot it, on the corner, marked "pivot" it gives you angles or roof pitches etc.."
I go "Let me see that thing!" Of course I've used one before, but only to cut square ends, so I never paid any attention to the rest of the numbers. He says "Yah, you get a book with it and it tells you all about it." I go " Mine never came with a book!" "I'm still a dummy on this thing!"

AH HA! What I finally realized was this:
I come from a drafting/architectural/ cabinet maker, woodshop, background.
He comes from a rough carpenter/ framing background, but he's a great cabinet maker too.
So, it's the way I learned vs the way he learned.
I always worked with drafting triangles, 30 degrees and 45 degreees,and a protractor, so everything was always measured in terms of the included angle.
He worked with that "speed square" which measures away from 90 degrees, like a miter saw, and has the roof pitch values on it . A 7/12 roof pitch is the same as a 30 degree angle. So, it was second nature to him to cut angles on the miter saw.
So, back to my original reason for posting, and I do appreciate your comments Mikey, for those starting out with some of these tools to immediately grasp the concepts behind them might take some 'splainin Lucy. Regards back to you! bill