Comment by zokier

The thing that piqued my curiosity was this note from the paper:

> This strongly suggests that the recommended frequency value for the secondary representation of the second is offset from the unperturbed transition frequency by approximately twice its assigned uncertainty of 1.3×10^-15.

> the recommended frequency value is strongly dominated by a single absolute frequency measurement [53], which in light of recent results is to be considered suspect.

So I guess we don't have a usable theoretical reference value here.