... .2).Measure angle 0°~270°,based on B ruler on a need checking plane, turning T ruler till the centre level vial ... ).Measure across angle from 0° to 270°only based on B/T ruler on each checking plane, the finger indicate the across ... needed.4).Measure level(0°) and plumb(90°) based on T ruler seeing 2 level vials,tolerance of accuracy:0.057 ...