""The clock in your sat nav is deeper in the Earth's gravitational well than the clock in the satellite so runs slower. If the programme didn't allow for this there would be an error of something like ten miles. Newton's theories are very, very good but there are real life situations where they give the wrong answer.

As a theory of pure science, General Relativity gives an entirely different description of how the Universe works. It supersedes Newton.""

I never knew that.

One of the joys of Mudcat is learning most unexpected things from people of whose knowledge and skills one was unaware.

Don T.