Because of some reasons, rack can not be measured by three coordinates or coordinate boring and other precision equipment, we can only consider using existing tools to meet the technical requirements of field measurement. Measure the end face pitch of the inclined rack according to the formula PN = Πmn / cos β F, but the tool room can only provide 0-500 vernier caliper. Because the total length of the rack is L = 6000, we generally do not consider measuring with a tape measure. In order to effectively, economically and precisely measure the spiral angle of the inclined rack, the ball method is applied, as shown in Figure 4.3: