A new and important numismatic method which has been developed since the end of the last century is to try to identify the individual dies from which a series of coins was struck by comparing as many as possible of the surviving pieces. Obverse and reverse dies deteriorate at different rates, and they break and are replaced at different times. It is therefore possible to establish sequences of die links for specimens which share a common die, and the order of the dies within the sequence may be determined by careful study of the progressive wear of a given die as it is exhibited through successive strikings. In this way many series have been classified and the relative chronology of issues established, providing a detailed understanding of how certain mints operated. In applying this method it is usually taken for granted that if two coins can be shown to be the product of the same die, they were struck at about the same time and in the same place. What, however, is meant by ‘the same time’? Surely not necessarily ‘within one day’ or ‘within one week’? Surely not necessarily ‘within one day’ or ‘within one week’? Most scholars would probably agree that even a month may be too brief a span for many issues. But what then? Several months, a year, several years, even decades?