In Belfast, a major radiocarbon calibration program was carried out between 1975 and 1985, by which radiocarbon dates calculated from estimated residual radiocarbon activity in organic samples were calibrated against the absolute calendrical timescale offered by tree-rings, or dendrochronology. This program is described in all its stages and both the shortcomings of the method and its technical possibilities are discussed. It is now technically possible to measure radiocarbon activity very accurately, but existing routine radiocarbon dates are still inadequate. The way to overcome errors in research results are explained and a notation system aimed at avoiding ambiguity is proposed. -- AATA