Thanks for this site information. I have visited this previously but did not quite get what I wanted. I have, however, discovered the information in the IESNA nineth edition reference errata, available on their website in PDF format. This confirmed that there were errors in their origonal text and was what was so confusing. Thanks for your reply anyway. Also we have recently built a goniometer for an imaging photometer so will be able to have results as soon as some other equipment of ours is repaired.