The OSGB36 vs WGS84 Legal Standard
The UK Ordnance Survey National Grid (OSGB36) was originally based on the Airy 1830 ellipsoid. Modern GNSS systems natively output WGS84 (or the European realization, ETRS89).
If you naively plot a WGS84 coordinate onto an OSGB36 map without an official transformation, an absolute positional error of approximately 100 to 130 meters will occur, depending on localized grid distortion. Ordnance Survey mandates the use of the OSTN15 grid transformation to mathematically map ETRS89 geometries onto the OSGB36 standard, ensuring civil scale compliance across the mainland.
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The Cumulative Boundary & Engineering Rework Exposure: NAD83 vs WGS84
Because the North American Plate moves ~2cm/year, NAD83(2011) and WGS84(G1762) currently diverge by over 2.2 meters. Using a "standard" GPS WGS84 coordinate for a high-precision NAD83 cadastral staking has triggered Boundary Dispute Geodetic Offset claims for foundational rework and utility misplacement.