This conversion calculator is provided as a convenience to facilitate access to vertical measurements that have been independently verified and are freely available from either NOAA CO-OPS or NOAA NGS. For rigorous emergency, planning or construction purposes, users are strongly advised to consult these original sources to ensure accurate and up-to-date transformations. All calculations are based on single tide station offsets; elevations obtained using this method are only valid in the immediate vicinity of the original tide station.