ChD 21 November 1990. Originating summons by which the lessees (H) sought a declaration on questions of construction of a rent review clause. The broad intention of the parties was that the proportion borne by the ground rent of £28,000 to the rack-rental of the building should be maintained throughout the term of the lease. This was determined by a formula whereby the reviewed rent was to be equal to £28,000 multiplied by a fraction of which the numerator would be the market rental value at the date of review and the denominator would be the initial rack-rental value. Questions arose in regard to the ascertainment of the market rack-rental at the date of the review. The building was intended to be occupied by a number of different subtenants. ChD held that the rent should be ascertained by considering the value of the premises on a hypothetical vacant possession basis. It was however to be an investment rent , based on the rent that could be obtained for the premises as a whole or i