Mean L-band visibility (averaged between 3.1 and 3.8 μm) for the K0-G2 baseline plotted as a function of time for a full night on December 9, 2018. The science objects are shown in orange, and the calibrators are in grey. The estimated transfer function in visibility (i.e. corrected from the partial resolution of the calibrators) is shown in blue. The variation of the transfer function represented by the modulation of the blue dots is a slow temporal variation.