30
Error Sources Associated With Differential Leveling
                      Error Source                    Typical Size of Error
                                                                in mm Per 1 km Section
›Systematic Errors Continued:
›
›Collimation ……….. ……………………………………….   2.4
›Under and over compensation …………………………..        0.4
›Refraction …………………………………………………..   2.0
›Refraction change during setup ………………………….       0.6
›Diurnal Earth tides …………………………………………    0.1
›Earth’s magnetic field ……………………………………..    1.0
›NI 002 parallax …………………………………………….    0.6