Geodesy.
The longitude of the datum origin equates to a value for the Ferro meridian of 17°40' exactly west of Greenwich.
Definition: JSON
{ "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json", "type": "GeodeticReferenceFrame", "name": "Militar-Geographische Institut", "ellipsoid": { "name": "Bessel 1841", "semi_major_axis": 6377397.155, "inverse_flattening": 299.1528128 }, "scope": "Geodesy.", "area": "Austria.", "bbox": { "south_latitude": 46.4, "west_longitude": 9.53, "north_latitude": 49.02, "east_longitude": 17.17 }, "id": { "authority": "EPSG", "code": 6312 } }