For true enlightenment, go first to the Royal Institute of Navigation website at . .. .<a href="http://www.rin.org.uk" target="_blank">http://www.rin.org.uk</a>. .. .then go through to the Satellite Navigation Forum and post the question there. Be warned though, they're very straight laced and take their navigation seriously. Wind-ups are unwelcome.... .. .**********************************. .Through difficulties to the cinema