Excavation Unit Datum Elevation

The datumElevation of an ExcavationUnit is the height of the unit's datum point, the local benchmark you measure down from when recording depths. Every depth in the unit — the currentDepth of excavation, the top and bottom of each StratigraphicLayer, the elevation of an artifact — is taken relative to this datum, so setting it correctly is what lets all those vertical measurements be compared across units and tied to a real-world elevation. Establishing a clear datumElevation for each unit at the start of work prevents confusion later when you reconcile profiles and build a stratigraphic model for the whole site. The field is optional but is standard practice for any unit with vertical control.