More accurate polynomial transformations between Greek / Hatt projection zones and GGRS87 / Greek Grid are available from the Military Geographic Service.
Hellenic Petroleum
2011-07-20
Geodesy.
See CRS code 4120 for recommended coordinate axis representation for the human interface.
Ellipsoidal 2D CS. Axes: latitude, longitude. Orientations: north, east. UoM: dec deg