I agree that we can assume any necessary discussion took place in order to reach agreement. However, the original is not very clear about whether "to be agreed" refers solely to the decision about which assemblies should be inspected or to "inspection" in all its aspects. The insertion of "to be determined" may have been an attempt to clarify this.
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SnappyThe equipment shall be used for the airtight inspection of delivery pipe assemblies (hereafter referred to as workpieces) to be agreed with you.I am curious about the phrase "airtight inspection".