  We report the direct comparison between the stabilities of two mobile
absolute gravimeters of different technology: the LNE-SYRTE Cold Atom
Gravimeter and FG5X\#216 of the Universit\'e du Luxembourg. These instruments
rely on two different principles of operation: atomic and optical
interferometry. The comparison took place in the Walferdange Underground
Laboratory for Geodynamics in Luxembourg, at the beginning of the last
International Comparison of Absolute Gravimeters, ICAG-2013. We analyse a 2h10
duration common measurement, and find that the CAG shows better immunity with
respect to changes in the level of vibration noise, as well as a slightly
better short term stability.
