+1 on spoke windup. If you ever build up a wheel with aero profile/bladed spokes, you will get an idea on how much a spoke can wind up when you tension them as you will see the twist on the bladed spoke really easy. On plain, non-bladed spokes, it is harder to tell if they are twisting but sometimes you can detect a twisting pattern on the legnth of the spoke as there are subltle markings and a a sort of grain that follows the legnth of the spoke. Best thing to do is to have your fingers of your free hand on the spoke right below the nibbple when you turn the spoke wrench and you will have an idea if it is twisting and how much you have to turn back the wrench to undo the twist after each tightening turn of the spoke wrench.
Chombi