"They are measuring 39:61 over a fieldwork period from mid-May to mid-July"
I.e. before 'the debate' which either damaged Yes or made more people realise 'it's not just about Salmond/SNP'.
But what about the DKs? The Naughtie/Radio4 prog (http://www.bbc.co.uk/programmes/b04d4qpb) - not 'representative' of anything - had about 1/3 of audience saying they were undecided. Several people apologising for not having made up their minds!
Someone said 'it'll all be decided in the last 2 seconds' - when people had the pencil in their hands.
(I've said several times, some people will decide when they read the question on the ballot paper).