What's the difference between the three or four leveling survey and the general level measurement?
External measurement accuracy requirements are different. The horizon difference and horizon difference cumulative value requirements are different, the difference of red reading and two height difference requirements are different.
The measuring methods are different. The ordinary level one side ruler will do, while the three or four level requires the double ruler to be measured according to "before, before, after" and so on.
Different instruments: measuring three levels of measuring instruments should be better than the average level of the instrument used (four level, you can use S3 level)
