Source: NOAA, Center for Operational Oceanographic Products and Services The term Mean Sea Level (MSL) can also refer to a tidal datum, or frame of vertical reference defined by a specific phase of the tide. Tidal datums are locally-derived based on observations at a tide station, and are typically computed over a 19-year period, known as the National Tidal Datum Epoch (NTDE). The present 19-year reference period used by NOAA is the 1983-2001 NTDE. Tidal datums must be updated at least...