Soundings are measurements of the water's depth.  They are collected at different points in the tide cycle and must be corrected so they all relate to a common reference point.  Several methods are used and you must check which one your chart and tide tables are using.  Methods are as follows:                                        ( Go Back ) 
   
bulletMLLW:  Mean Lower Low Water is the average of the lowest of the two daily tides.  This is the most common method of reporting soundings on US Charts
 
bulletLAT:  Lowest Astronomical Tide is the theoretically lowest water level achieved by astronomical influences.  This method is used in Canada and in most hydrographic offices around the world.
 
bulletMLW:  Mean Low Water Level is the average of all the low tide levels.  This method is found on some older US East Coast Charts.
 
bulletMLWS:  Mean Low Water Springs is the average of the spring tide low waters.

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