120° is the best way to measure deviations, checking at every 90° with symmetrical, equally sized rotating parts is simply remeasuring at two points (0/360° - 180° and 90°-270°) if it deviates +0.010 at 270° it will basically be out -0.010 at 90°. @ 120°, 240°, and 0/360° when alignment deviates +0.010 @ 0/360°, it will be out - 0.005 @ 120°, and -0.005 @ 240° if horizontal elevation alignment in either shaft is off and lateral alignment is < 0.001 If @120° the deviation is -/+ 0.005 rotate the coupled shafts 90° and repeat if measurements are the same, align the misaligned machine, if they are different, address the off center rotation or bend in the relevant shaft.