What is the 'zero tide' on a tide table? This is the original question, but I can't answer it because I don't know what a zero tide is: (Using a tide table): If an organism were located at a tidal height of 1 m above zero tide, how do you determine how long (in hours) it is exposed to the air? Any help will be appreciated!

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The zero tide level on a tide table is the baseline level assigned the height of zero from which all other tide levels are measured.  The zero tide level for a given area is calculated by averaging the height of all of the lowest tides for that area over a certain period of time.  Once the average water level height has been determined, it is set to zero and all of the other water levels are baselined from that level.

I would assume that the best way to answer the question is to find the lowest tide over the course of a 24 hour day (called low low tide) on the tide table that you have and assign that as zero tide.  We are told that the organism sits 1 meter above this level.  Then, find the amount of time that the water level is between the zero level and 1 meter above that, and that is the amount of time that the organism is exposed to air.

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