Denim Finishing
Leg twist is not a sewing fault. It is twill torque, and it has to be cancelled in finishing before the garment is ever cut.
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Total skew the finishing range must set
The torque coefficient depends on twill direction, weave, yarn twist and how hard the garment is washed, so it must be measured on the actual construction — a right-hand and a left-hand twill of the same weight will not share one. Over-skewing to chase a difficult wash produces visibly bowed pockets and hems.
Denim Skewness & Leg Twist Correction Calculator — free, with the formula and a worked example, at Textile School.