There's no perfect method. What is important is to have a system and
stick to it but if yopu want your data to be comparable to that from the
majority of other stations then the 0900z-0900z system is the one to
use.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England

Could you remind me if that's recorded under the date of the start or the
finish of the period for both

Thanks
Dave.