Hi Andy
Yes I agree about the refererence star at same altitude although I can`t always find one ;-).
Have you tried the reference star spreadsheet for spectro mentioned on the spectro-aras forum here
http://www.astronomie-amateur.fr/Documents%20Spectro/ReferenceStarFinder.xlsm
I`m using Open Office and couldn`t quite get it to work properly but I`ll stick with it!.
Hopefully stuff like this will be covered at Sidmouth, you got your presentation finished ok?
cheers
Steve