Complex sentence: The rows of the symbol cycle through the three clusters, so row 1 uses patterns from cluster 1, row 2 uses cluster 2, row 3 uses cluster 3, and row 4 again uses cluster 1.
Split into simpler sentences: The rows of the symbol cycle through the three clusters. Row 1 uses cluster 1, row 2 uses cluster 2, row 3 uses cluster 3, and row 4 returns to use cluster 1.