In this method, you shift the origin of one datum relative to the other using translations along each axis. Those shifts are the origin offsets, and there are three of them—one along X, one along Y, and one along Z. Since this approach includes only translations (no rotation or scale), the total number of origin offsets is three.

When reporting positional accuracy for primary horizontal and vertical control, two levels are used: local accuracy and network accuracy. Local accuracy describes how well points within the local control network agree with their positions in the local frame—it's about the precision and consistency of measurements within a localized area. Network accuracy, on the other hand, assesses the overall quality of the control network across a broader region, reflecting how well the network ties into the larger reference framework and how errors propagate across the network. Reporting both conveys that the local network is precise while the network as a whole remains consistent across the wider area. Other statistics like RMSE, confidence intervals, or standard deviation are useful metrics, but they don’t capture this two-tier reporting approach that specifically characterizes primary control networks.

Height of Instrument is the vertical distance from the reference datum up to the instrument’s line of sight. This value represents how high the instrument is positioned above the datum and is the constant you use to convert rod readings into elevations. You determine it by taking a staff reading on a point of known elevation and adding that reading to the known elevation (HI = known elevation + staff reading). Then any point’s elevation is found by subtracting that point’s staff reading from HI (Elevation = HI − reading). This definition directly captures what HI measures—the height of the instrument’s line of sight above the datum—unlike rod readings or intermediate placements, which describe measurements or locations rather than the instrument’s height.

The network positional accuracy is about how uncertain the computed coordinates of a control point are after the network is adjusted, relative to the geodetic datum. This uncertainty comes from the propagation of measurement errors through the network solution, and it is usually expressed as a 95% confidence region (often a 3D ellipsoid) around the point’s coordinates. In practice, the smaller this accuracy value, the more precisely the point’s position is known with respect to the datum. It’s not about how long the point’s coordinates stay the same over time, not about how far apart control points are from each other, and not about the precision of the surveying instruments themselves—those relate to stability, point density, or instrument capability rather than the resulting coordinate accuracy within the datum.