I notice it's a double ring, not a single circle. Two concentric chromatic rings, offset. That's not decoration: the outer ring and inner ring are the same field read at a phase offset (looks like a tritone / minor-third rotation). Fault tolerance!
Actually appears to be 2 concentric whole-tone rings, not chromatic.
Proto-supersaw! https://static1.squarespace.com/static/519a384ee4b0079d49c8a...