Sorry did not see this in time but in case someone else does not know:
What you need for measuring with the KC
Dogs KC name and Number
Microchip number / tattoo number or if niether a small photograph
Ideally a record book - can be ordered from the KC for £1.50 and I beleive if you only order one there is no postage - go to KC website, find the shop and do a search in there
There is a possiblity that measurers will have some spare record books but this is not guaranteed and if you are later on the session there may not be any left. Also it is easier if you have the book beforehand and can fuill in details then you do not need so much paperwork with you. If you belong to a club then some clubs hold a stock of them (I know we do) so that when we advise members to be measured we sell them a book to ensure that one is avilable.
Other points should you feel your dog is borderline - make sure all excess fur is trimmed from the feet and nails are short. Also advice would be to give the dog a good run to ensure they are relaxed for the measure. This is only handing on advice I was given - It will not noticaebly affect the height of your dog but if you have a borderline small medium dog if might help not tip the measure!!