Choose between Mean Sea Level (MSL) and Lowest Astronomical Tide (LAT)
The height of a water level, must be specified relative to some other level and this level is called 'the datum'. If you measure the height of an object it's height would usually be given relative to the floor on which the object is sitting. In this case the datum is the floor and it is usually obvious what the height is measured from so is not explicitly stated. However with tidal levels the datum must be specified as there are numerous possible datums that could be used when giving the height of the tide.
For tidal levels offshore, mean sea level (MSL) is most often used as the main datum. Alternatively, Lowest Astronomical Tide may be used as this can be estimated from
a set of observations or tidal records.
Always check your datums are consistent and stated when using predictive tidal data operationally.