Every pendulum here obeys the same equations and starts from the same place — except that the lower arm of each one is turned a further epsilon (a ten-thousandth of a radian by default) from its neighbour. For a few seconds they are one pendulum. Then the difference doubles, and doubles, and the garden flowers. Nothing is random: the same start, the same epsilon and the same count always give the same bloom.
Spread is the widest distance between any two tips, in arm lengths. Split is the moment it first passed 0.1.