用外圆找中心点和用内圆找中心线,用以往的办法划线,既费时间,又不准确。这种中心规(图1)是根据圆上任意两点的中垂线通过圆心的道理制成的。可用来找φ40～φ250毫米范围内的内孔或外圆中心,使用时,只要将两短 Find the center point with the outer circle and use the inner circle to find the center line, crossed with the past approach, both time-consuming and inaccurate. This center rule (Figure 1) is based on the principle that the perpendicular bisector of any two points on the circle passes through the center of the circle. Can be used to find φ40 ~ φ250 mm within the hole or cylindrical center, when used, as long as the two short