1.6180339887...

A blustery day today - looking out the window at the trees tossing about, for some reason started thinking about good ol' Fibonacci.
So here's the spiral that bears his name.

The basic maths is:
a+b:a = a:b
or
(a+b)/a = a/b = 1.6180339887...

Otherwise known as the Golden Ratio (among other popular names). Boffins love it. So do artists - although they don't necessarily appreciate the maths of it in quite the way boffins do.

Please note that I am not in any sense a mathematical boffin. I just like the pretty curl...