The handwritting is something I would expect from an architect or engineer, very precise - note how many corrections there are (none)... this is bery clearly annotated and laid out.

I have no idea what it means, but the spiral caught my eye, with the precise dividers thin-thick-thin, same style used on the first triangle.

It made me think of a tone, starting quiet, becoming intense, then fading...

Just my gut response to these images.