Refining the evaluation of uncertainties in [UTC - UTC (k)]

We refine the evaluation of the uncertainty on [UTC - UTC (k)], by taking into account in particular the contribution of the correlations. To easily handle the different computational requirements we use a matrix formulation. Using this matrix formalism we re-analyze the link-based uncertainties and we obtain the same solution as given in [Lewandowski, 2004]. Next we evaluate the site-based uncertainties and compare the results with the link-based uncertainties