Complex sentence: More accurate methods for determining the preload rely on defining or measuring the "screw extension"; for instance, measurement of the angular rotation of the nut can serve as the basis for defining screw extension based on the fastener's thread pitch.
Split into simpler sentences: More accurate methods for determining the preload rely on defining or measuring the "screw extension" from the nut. Alternatively, measurement of the angular rotation of the nut can serve as the basis for defining screw extension based on the fastener's thread pitch.