List of centering errors (SDO and SDT)

The centering error is the error made in plumbing instruments and targets over the station marks.

The estimates vary from 0.2 cm in cases where instruments are set on ordinary tripods directly above well defined station marks using plumb bobs or T2 tribrachs to 0.5 m in cases where targets are poorly defined such as square grain elevators with peaked roofs.

The estimates for centering error are included on the standard deviation records for directions, lengths and azimuths. (SIGMA records, code 51, 52 and 53)

• SDO is the centering error in cm at the observing station
• SDT is the centering error in cm at the target station

        SDO     SDT     Description

        0.0     0.0     Forced centering (mekometer baselines)
        0.2     0.2     Tripods set over survey tablets
        0.5     0.5     Bilby triangulation towers, tellurometer
                        towers
        1.0     1.0     Aerodist
                5.0     Church spires
                10.0    Cairns
                10.0    Chimneys
                10.0    Light houses
                10.0    Stand pipes
                10.0    Water tanks
                50.0    Grain elevators