A short 2004 article by Ralph Griswold, part 6 of his T-Sequences series, on modular operations applied to t-sequences used in drafting. It explains modular reduction (shaft-modulo m) with figures showing a sequence reduced to 10, 8, 6, 5, 4, 3 and 2 shafts. It then describes modular expansion, the converse operation that removes wrap-around when converting a t-sequence on m shafts to n shafts, with a step-by-step procedure, an example and a summary of notation.