In the event of the revenue earned during the financial year most nearly concurrent with any period of insurance (as certified by the insured's auditors) being less than the sum insured thereon, a pro-rata return premium not exceeding 50% of the premium paid on such sum insured for such period of insurance will be made in respect of the difference.

    If any damage shall have occurred giving rise to a claim under this insurance such return shall be made in respect only of so much of the said difference as is not due to such damage.

    If the indemnity period under this insurance is 18, 24 or 36 months, then this clause is deemed to relate to one and a half, twice or three times the revenue earned respectively during the said period as appropriate