Science Explained: How does sat-nav work?

Satellite-navigation systems have become so common that we take for granted the technology - in space and here on Earth - that makes them possible.

Satellites, atomic clocks and good old-fashioned geometry fit into the equation.

But how do sat-nav systems actually work?

Professor Cathryn Mitchell from the University of Bath explains as she finds herself navigating around London.

Please note: The graphics used in this video are not to scale