While thus holding the disc down, rotate the rule so that its parallel longitudinal markings are parallel to the TN lines, with the variation indication line always on the N end of the rule.
Ngelixesha ubambe icwecwe ezantsi jikelezisa umthetho ukwenzela ukuba imimako emide efanayo ifane nakwimigca ye TN, ngotshintsho olubonakalisiweyo imigca soloko isesiphelweni somthetho u-N