How the sett is calculated

This uses Ashenhurst setting theory: sett equals wraps per inch times R/(R+I), where R is the ends in one weave repeat and I is the number of interlacements. Plain weave lands on half your WPI; twills and satins pack denser because they interlace less often. The firm-to-open range and cloth hand account for the fact that real sett depends on the fabric you want, the fiber, and finishing. It assumes a single balanced cloth, so it does not model double weave or supplementary structures.