What does NEC4 clause 60.1(8) mean?

In the NEC4 main contract the decision is the Project Manager's or the Supervisor's. On an NEC subcontract it is your main contractor's. Show two things. First, a decision given to you in the form the contract requires, which means in writing and separate from other communications. Second, a later communication that changes it. A decision is wider than an instruction. It includes accepting a design or a subcontractor, agreeing a method, or a decision on a test result. The clause does not ask whether the change was reasonable, only whether it happened. The fault filter comes at clause 61.4. So a decision changed because your own information was wrong gives no change to the Prices. Because the event comes from its own communication, your main contractor should notify it when it communicates the change. If it does not, you notify under clause 61.3, and the 8-week bar does not apply. The change to the Prices, your contract price, is assessed under clause 63.1. It is the effect on actual Defined Cost for work done by the date of the communication. Add forecast Defined Cost for work still to do, plus the Fee. So it covers the wasted work done on the first decision, as well as the cost of doing it the second way. Two things go wrong most. The first decision was only verbal, or buried in meeting minutes, and is then denied. Or you claim the whole cost of the second approach, not the difference the change made. Any delay to the Completion Date is assessed separately under clause 63, and that is a job for your planner.