A clause in a joint venture agreement providing that effective control must not be altered 'from that subsisting at the Commencement Date' operates as a benchmark for comparison on each occasion of alteration, not as a limitation confining the clause to a single operation. Where a primary judge fails to first identify ambiguity before resorting to commercial purpose, the appellate court may independently construe the clause but will uphold the result if the construction accords with commercial purpose.
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