Wiktionary
datum point
n. A point which serves as a reference or base for the measurement of other quantities.
Usage examples of "datum point".
They'd cleared the initial datum point, and the aircraft's crew would need a few minutes to evaluate their attack before beginning a new search.
We'll drop a buoy here, to use as a datum point, but I think we should search in a box towards the north-east, maybe a half-mile square.
He bit his lip until it hurt, focused all his attention on the displays, and waited for the next datum point on his decision tree.
The grid is laid out using spikes and string, then the squares of the grid are designated coordinates by counting the number of units-feet or meters (we use feet)-north and east of the datum point, which is located in the southwest corner of the site.