Computation of SDA for Direction Observations

Instrument                       Instrument Code                 SDA (sec)
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First order                          51Fxx                    0.6 x sqrt(16/N)
(Wild T3 or equivalent)

Second order                         51Sxx                    2.0 x sqrt(8/N)
(Wild T2 or equivalent)

Third order                          51Txx                    7.0 x sqrt(3/N)
(Wild T1 or equivalent)


After 1970:  With Geodetic Survey new observing procedures:

First order                          51Fxx                    0.6 x sqrt(24/N)
(Wild T3 or equivalent)

Second order                         51Sxx                    2.0 x sqrt(6/N)
(Wild T2 or equivalent)
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Note:  xx = number of sets
       N  = number of sets


Examples of instrument codes:

        51F16, 51F12, 51F08, ...
        51S08, 51S06, 51S04, ...
        51T06, 51T03, 51T01, ...