The word 'ascertain' in cl 44.6 of a standard form building contract (and by extension similar provisions) authorises the exercise of professional judgment and estimation, and does not require precise factual determination yielding one uniquely correct value. A party that elects to litigate the validity of a contractual determination on the merits, rather than insisting on compliance with contractual dispute resolution procedures, waives its right to rely on non-compliance as a bar to the challenge.
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