Comparison of 3 Absolute Gravimeters Based on Different Methods for the e-MASS Project

We report on the comparison between three absolute gravimeters that took place in April 2010 at the Laboratoire National de Métrologie et d´Essais. The three instruments (FG5#209 from METAS, Switzerland, IMGC-02 from INRIM, Italy, and CAG from LNE-SYRTE, France) rely on different methods: optical and atomic interferometry. We discuss their differences and their similarities. We compare their measurements of the gravitational acceleration in four points of the same pillar, in the perspective of absolute determination of g for a watt balance experiment. The three instruments performed repeatable g measurements but do not agree at the level aimed for. This work calls for additional studies on systematic effects.