What does NEC4 clause 60.1(6) mean?

Clause 60.1(6) gives teeth to the contract's reply periods. The event is that the Project Manager or the Supervisor does not reply to a communication within the period required by the contract. The contract requires replies to many communications, and the period is either the general period for reply stated in the Contract Data or the specific period a clause gives, such as the two weeks the Project Manager has under clause 62.3 to reply to a quotation. The paragraph is about a reply that is late or absent, not a reply the Contractor dislikes; a reply within the period that refuses acceptance is dealt with, if at all, under clause 60.1(9). To rely on the paragraph the Contractor shows the communication it sent, that the contract required a reply to it, the period that applied, when that period ended and that no reply was received by then. The Contractor notifies the event under clause 61.3 within eight weeks of becoming aware, which is the day after the reply period expired, not the day the late reply arrives. Several late replies have their own remedy, such as the treated acceptance of a quotation under clause 62.6 once the Contractor has notified the failure, and the compensation event covers the cost effect those mechanisms do not. The change to the Prices is assessed under clause 63.1 as the effect of the late reply on actual Defined Cost by the date of the notification and forecast Defined Cost afterwards, plus the Fee, in practice the cost of work held while the reply was awaited. What most often goes wrong is that the Contractor cannot show when its communication was received, or the cost claimed was incurred before the period expired and would have arisen anyway. Any delay to the Completion Date is assessed separately under clause 63 by the programming expert.