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The phase dependence constraint triggers the scheduling of observations at specified times of particular astronomical interest. However, instead of specifying time absolutely (as is the case for coordinated observations) time is specified in terms of phase by giving the epoch (in modified Julian days) and the recurrence period of the event (in days). A suitable observing window satisfying the specified phase constraint as well as all other general viewing constraints will then be selected. If the requested number of observations is more than one, the requested observations will be scheduled spaced by the specified period, dividing the requested observing time approximately equally among the individual observations. In order to avoid loss of accuracy the epoch should be given as nearest epoch prior to 1 August 1991 in modified Julian date where ( ) and the phase must be given with an accuracy sufficient to allow extrapolations over six months; note that barycentric corrections are not important for scheduling such observations.