A teaching-oriented article from Master Weaver (Fulford, Quebec) on how to choose warp yarn and sett. It explains why yarn count does not give a fixed thickness, why sett formulas are unreliable, and how to find the lower and upper sett limits for warp-face, 50:50 and weft-face fabrics. It gives a simple rule, S = k√C, with coefficients for cotton, wool and linen, and a graph of the lower limit of sett by yarn count. It recommends that students make and keep sample swatches on small frame looms.