I had a moment with a pillar and a photo and a friend in Clare Suffolk

A little light bulb moment... The sort that serendipitously sleets through your consciousness and lodges between your ears.

I was looking at a photo sent to me by a fellow graffiti hunter and friend. Her name is Pat May and she takes some good photos, as well as being a very prolific graffiti hunter....
I wanted a photo of some cubes, because I was trying out an idea and so I asked her for an image. What she sent me was the wrong photo - but then it became the *Oh so right photo* almost instantaneously.
The church is in Clare and the graffito is half way up a pillar in the northern arcade, close by the chancel if you want to go and take a look.
It is confusing, but obviously drawn with purpose.
Can you see it yet?
It is Euclidean geometry, great, glorious geometry

Now I was always rubbish at maths - truly terrible at the subject, so I never thought that I would be describing this formula as glorious.

It describes how the angle at point J (which in this case is 45 degrees) is half the angle at b (90 degrees)

The maker has drawn the central line running vertically first and placed the two arrow heads pointing directly up and down. Then they have repeated this process, but horizontally aligned.

Finally they have done the same in the diagonal, using the base of the arrowheads as the reference point.

My Gestalt didn't disappoint; my only query is, why did someone with obvious geometrical learning not use a straight line to draw a formula which demanded straight lines?