There are about a dozen points in the world ocean where the tide simply pivots around a still centre, and the range there is close to zero.

The tide rotates around these amphidromic points like the hand of a clock, high water sweeping round the rim while the middle barely moves. One sits in the North Sea off Norfolk, which is why tidal ranges vary so wildly around the British Isles — from over twelve metres in the Bristol Channel to under a metre near the pivot.