Throughout the natural world, the ratio of Phi (2:3:5) remains an underpinning 'secret maths' that is at the same time both both obvious yet mysterious. Known as the Golden Section, its numbers extrapolate themselves simply by a very particular ratio, which is close to but not the same as a 'thirds' logic... To see it in action, take a spiral such as an unfolding fern. Add any two consecutive numbers (say 2 and 3) to create the next one (5). Then pick up the previous one (3) and add this to the 'present' one (the 5) to create the following one (8).... this logic is consistent whatever the size and demonstrates a fundamental principle of the natural world.