Is there a standard 'sea level', or does it change with the daily tides?

Question

If there is, it's probably near London!

Answer 1

Engineers use mean lower low.

There are 2 highs every day and 2 lows.

The average of the lower lows is used as a datum.

It is not quite the same a mean sea level as found on maps.

Answer 2

There is a standard ' Mean Sea Level' used in the U.S. for all altitude measurements.  See below.  Other countries have their own standards.

Answer 3

There is no standard sea level. The sea level mostly rises nowadays because of the consequences of global warming.

Take a look at the website below!