Fourth International Comparison of Absolute Gravimeters

In 1994, from 24 May to 8 June, the fourth International Comparison of Absolute Gravimeters was held at the Bureau International des Poids et Mesures, S?vres, France. Eleven absolute gravimeters were operated at five sites and then compared by means of a high-precision gravity network which was itself observed throughout the period. The results demonstrate that absolute gravimetry can be carried out to an accuracy of 3 ?Gal to 4 ?Gal, which represents a substantial improvement since the first international comparison (1981, 10 ?Gal). The relatively low rate of improvement, one third of an order of magnitude in fifteen years, is certainly limited by current technology for measuring small time and space intervals. A notable finding of the comparison was an unsuspected source of systematic error which can be eliminated by new hardware or corrected through a correction algorithm.