Snowflake rule
One number in a rule for freezing vapor decides whether a seed of ice grows into a needle or a six-armed star.
The crystal is a model: Gravner and Griffeath's 2009 rule, run from the paper on a lattice 181 cells across. Its dials are the rule's own numbers, and the first plays the part temperature plays in real air without being one. Color shows when the ice froze. Beside 60,274 snowflakes photographed falling, the air at the camera did not tell plates from columns, so no measured flake is placed here.
Rule: Gravner & Griffeath 2009, three-dimensional snow crystal growth, reimplemented from the paper.