additional runs are made due to excessive divergence in a second-order section of a level line, the
rejection limit of individual values from the indiscriminate mean of all measurements is ...9 millimeters
√K.
(2) Class II is used for the development of nets in more accessible areas. The criteria for Class
II are the same as those for Class I except that Class II lines are single run (in one direction only). The
AE formula is still ...8.4 millimeters √K, where K is the length of the line in kilometers, the line being the
distance between ties to existing benchmarks.
PART B: PRECISE DIFFERENTIAL LEVELING
4-4. General. In principle there is no difference between precise and ordinary differential leveling
(Figure 4-1). In ordinary differential leveling, the distances run between checks are relatively short and
with the usual precautions, and the results are sufficiently accurate for general-purpose surveys. Since
very small errors cannot be detected, the relative coarseness of the determinations may, through
compensation of errors, give some degree of accuracy. In precise leveling, the circuits may be of
considerable length; therefore, operations must be conducted so that the uncertainty of each individual
determination, as well as the actual closing error, is reduced to a minimum. This necessitates the use
and proper handling of precision instruments and precise rods.
Figure 4-1. Direct Differential Leveling
EN0593
4-4
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