  We present a 27-days long common view measurement of an absolute cold atom
gravimeter (CAG) and a relative iGrav superconducting gravimeter, which we use
to calibrate the iGrav scale factor. This allowed us to push the CAG long-term
stability down to the level of 0.5~nm.s$^{-2}$. We investigate the impact of
the duration of the measurement on the uncertainty in the determination of the
correlation factor and show that it is limited to about 3\textperthousand~by
the coloured noise of our cold atom gravimeter. A 3-days long measurement
session with an additional FG5X absolute gravimeter allows us to directly
compare the calibration results obtained with two different absolute meters.
Based on our analysis, we expect that with an improvement of its long term
stability, the CAG will allow to calibrate the iGrav scale factor to better
than the per mille level (1$\sigma$ level of confidence) after only one-day of
concurrent measurements for maximum tidal amplitudes.
