Radiocarbon measurements have been performed on a 250 year 'floating' tree-ring section recovered from an archaeological site in north-east Scotland. Short term fluctuations in atmospheric 14>sC concentration appear to be superimposed on a general trend of decreasing ambient 14>sC parallel with tree growth. The most significant finding is the range of dates obtained from the sequence, namely 400 years, since it implies that the error on a single radiocarbon date is considerably greater than at present accepted on the basis of analytical precision alone. -- AATA