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 concentration appear to be superimposed on a general trend of decreasing ambient14Cparallel 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 precisio