How are the delay damages reduced if the Employer takes over a part of the works before Completion?

How are the delay damages reduced if the Employer takes over a part of the works before Completion?

The Project Manager assesses the benefit to the Employer of taking over the part of the works as a proportion of the benefit to the Employer of taking over the whole of the works not previously taken over. The delay damages are reduced in this proportion (see Clause X7.3).