What is Muse actually measuring when you're in a state of "calm"?

I’m having a hard time finding information on what Muse is actually measuring. When you’re going into a state of “calm” is it detecting alpha dominance? Thanks for any help!

I have this question also. I hope someone can answer.

Calm is a mix of alpha and theta. Active is beta. Neutral is a mix of beta and alpha. At least this is what I think based on my experience with the Muse band and my layman’s understanding of brain waves.

I’m not sure how gamma enters into the picture.