There are many conflicting opinions on what relaxation looks like and Interaxon are keeping their algorithm a secret. In my opinion high relative Alpha looks like a good candidate. This means high Alpha and/or lower other waves.
If you want a deep dive in this theory, check out the research paper "My Virtual Dream: Collective Neurofeedback in an Immersive Art Environment" by Natasha Kovacevic, Petra Ritter, William Tays, Sylvain Moreno, Anthony Randal McIntosh:
http://journals.plos.org/plosone/articl ... ne.0130129
For a more basic guide, have a look at Interaxon's beginners guide to brainwaves:
https://choosemuse.com/blog/a-deep-dive ... plained-2/