Thanks Mr Bristol? JBA, I think we may be looking too deeply at this - perhaps it is best to refer back to your provider as it is likely to have caused confusion before by the sound of it. If Dick is Mr Whittingham Senior then I suggest his opinion trumps all of ours! Sometimes altimetry questions are related to a particular part of the syllabus and I know I often complicated things by looking at the wrong part. I will watch with interest...