Proposed revised definition for Mean Sea Level (MSL) in line with IHO Resolution 3/1919, as amended, was finalized at TWLWG 6:
Mean Sea Level: The average height of the surface of the sea at a tide station for all stages of the tide over a 19-year period, usually determined from hourly height readings measured from a fixed predetermined reference level (chart datum). Proposed:
Mean Sea Level: The average height of the surface of the sea at a water level station, determined from height readings measured over an appropriate period of time from a fixed predetermined reference level (chart datum).
I am glad TWLWG 6 could achieve a shorter definition and get rid of hourly height measurements, which do not mean much with modern tide gauges.
However, I regret the 19-year period.
Do you know what they did with the previous lengthy complements?
It was agreed the additional information included in the original 'long' version would be better included in a publication such as C-13. The 19-year period was retained, after much discussion, due to the recommendation to cover a complete luna cycle.