What decides what sea level is?
Question
What decides what sea level is? Surely the level of the sea changes all the time.
Mark, Marble Arch
Answer
** Definitive ** REVOKED!
Name: Martin, Woolwich
Qualification: Plumber
Answer: When I was in college, we were told that all UK sea level readings are taken at Newquay. So when a surveyor puts a mark on the road and measures sea level, it takes it from Newquay in Cornwall.
** Definitive **
Name: Richard, Hertford
Qualification: Boat Handling course, bit of diving
Answer: The sea level in the UK is measured in Newlyn in Cornwall, not Newquay. I believe the global sea level comes from this place.
Name: John, Coulsden
Qualification: Clearly not quite enough!
Answer: It's based on what they call Mean High Water Springs, which is an average level of the high water tides. All heights on maps are based on these measurements.
(James O'Brien: But it's different around the world. Is there not one place where it's measured from?)
Name: Chris, Woolwich
Qualification: Sailor - I've been across the Atlantic a couple of times
Answer: It's related to the lowest astrological tides, which happen every seven years. It's based wherever you are, so if you're at the English Channel, the sea level is based on this for the English Channel. There is no objective sea level around the world, as it is all based locally.
(James O'Brien: Not definitive, but I'll give you a round of applause for sailing across the Atlantic!)