GPS/GNSS receivers determine very precisely positions on the surface of the earth. Geonet compute a daily position for each of their stations so we can track the deformation caused by the interaction of the Australian and Pacific tectonic plates.
Each day a reading of the station position is noted, this is called the “displacement from initial position”. The times used are UTC and the readings taken at 11:59:00UTC which equates to 11:59pm NZST (12 hours before UTC). This is then deducted from the previous days position, to determine the amount of movement in the 24 hours in mm. This may be +/- .

Each station is marked on the map at the base junction of the two arrowheads. The Red arrowhead points in the direction of movement up or down vertically.
The Blue arrowhead points in the direction of horizontal movement, which may be NW, NE, SW, SE. It is very rarely directly N,S, W or E.
Beside each station’s arrowhead set is a label with the direction (the letters U=up, D=down, W=west, E=east, N=north, S=south), and the amount of movement in mm.

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