Besides, according to the result of the calculating example, a discussion is made about how to determine the mean year of the different observation periods and how to choose the levelinglines.
此外，根据实例计算的结果，讨论了有关中心年代的选取以及观测路线的取舍等问题。
2
The hand guard helps with screw stabilization, houses a stud finder and a laser guide to project plum lines and assist with leveling.