Sixteen two-tone coloured, four-strand reef knots defined as unit cells that can be tiled together to create a countless number of knot patterns. Left column: the 16 knot units mathematically identified. Right panel: 24 two-tone knot patterns, each produced from knot units shown in the left column. The patterns whose number indications are in the same colour are figure-ground reversal. The pattern number indications with asterisks show that the same set of knot units can be tiled in multiple ways to create variations of knot patterns and structures. Diagram adapted from Nimkulrat and Nurmi (2019, p. 20); photographs and notations: Nithikul Nimkulrat.