  A method is presented for analysing over-determined sets of clock frequency
comparison data involving standards based on a number of different reference
transitions. This least-squares adjustment procedure, which is based on the
method used by CODATA to derive a self-consistent set of values for the
fundamental physical constants, can be used to derive optimized values for the
frequency ratios of all possible pairs of reference transitions. It is
demonstrated to reproduce the frequency values recommended by the International
Committee for Weights and Measures, when using the same input data used to
derive those values. The effects of including more recently published data in
the evaluation is discussed and the importance of accounting for correlations
between the input data is emphasised.
