The metrological assessment includes the evaluation in terms of absolute frequency accuracy and stability. The traceability chain is provided thanks to the availability of a frequency comb, an ultrastable laser source (a state-of-the-art narrow < 10 kHz linewidth tunable laser, optionally reduced to < 1 Hz by stabilization to a superior cavity-stabilized laser at 1156 nm via an optical comb), a primary frequency standard (Cs fountain IT-CsF2) and Yb-optical (IT-Yb1) clock. Both IT-CsF2 and IT-Yb1 are continuously operating clock metrologically assessed and they regularly provide calibration for the Atomic Time Scale.