I really like this graph, it was a nice find. Thanks for posting!

Actually I took for granted that Pims suggestion was correct. But it is only correct if the triangle intersect at the very precise same coordinate - as the circles intersect. (…and as fas as I can tell after calculating on it - they do?)

Radius of circles and their centerpoints

triangle segment as function:

Circle formula and substitution with

I added a diagram to with a symbolic interpretation rather than a color difference.

And, if an area had a resulting ++ or --, i.e 'double layers'

You'd had to calculate that area.