Each display equation uses 30-40 word equivalents, and our style is to avoid them in the main text unless they are newly derived (not relevant here) or crucial to the overall logical flow of the text. The definition (eq 1) of effective spin probably could be shifted to the Methods, with a brief description in words in the main text. I am open to persuasion that eq 2 needs to be in the main text, but probably it too can be shifted to the Methods.