55.Section 18 provides that where the whole or part of the chargeable consideration for a transaction is contingent, the amount of consideration should be calculated on the assumption that the amount relating to the contingency will be payable, whether or not the occurrence of the contingency means that the amount will be payable or cease to be payable. So where a contingency affects the eventual amount of consideration, buyers must calculate the consideration on the basis that the amount relating to the contingency will be payable. “Contingent” is defined in subsection (3).