It seems Field Maps now has the OSTN15 transformation available in the app (it was previously missing). If I set the Field Maps app location profile up correctly (GNSS coordinate system = GCS WGS 1984 4326; Map coordinate system: British National Grid 27700), and use a BNG basemap (e.g. GB Cartographic), it displays BNG eastings and northings for a point recorded in the app on my mobile devic. However, it doesn't seem to save the eastings and northings as fields in the hosted feature layer. So when I view the data in AGOL, or export it to a feature geodatabase or an excel file it only has lat and long coordinates. Does anyone know how to get it to save BNG eastings and northings?