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Error Sources Associated With Differential Leveling
                      Error Source                    Typical Size of Error
                                                                in mm Per 1 km Section
Blunders:
›Forward pin or plate movement between setups………      10.0
›One rod unit or larger error in reading the rod………..         5.0
›
Systematic Errors:
›Rod verticality error …………………………………...        1.0
›Rod scale error………………………………………….       2.0
›Thermal expansion of Invar rod ……………………….        0.2
›Rod index error ………………………………………..        1.0
›Movement of tripod during setup (if set up correctly)…       0.2
›Gradual movement of turning points:
›during setups ………………………………………………       0.6
›between setups ……………………………………………        0.6
›