Instability comparison with conventional clock CS2
In the following we denote with y the relative frequency difference between a clock and a reference standard, y = (fU - fR) / fR. The temporal variation of this quantity which is also called instability is described by the two-sample standard deviation σy(T). If it is calculated according to the relation
where yi (i=1...n)denotes the observed relative frequency differences over an aberaging time interval of length T.
The figure shows σy(T) for the primary clock CS2 and for CSF1. In both cases the reference is a hydrogen maser whose instability is lower than that of CSF1 for up to T ≈ 10000 s. At longer averaging times, σy is also influenced by the instability of the maser.
The figure can be interpreted as follows: For CS2, a frequency measurement with a relative statistical uncertainty of 1x10-14 takes more than one day. For CSF1, this measurement requires only 10 minutes.