Perpendicularity - is the condition of a surface, axis, or line, which is 90 deg. From a datum plane or a datum axis.
垂直度-条件是表面，轴，或线，这是90度的基准平面或基准轴。
2
The connection can be made by using the running surface of the paved cart as the horizontal datum.
连接时可以利用已铺好的大车运行轨道面作为水平基准。
3
Surface should be used as a fine datum to be processed first, because the precision of the positioning of the surface is more accurate, the smaller the clamping error is.