Lease Agreement Interpretation and Tacit Modification of Rent Adjustment Index

A contractual dispute arose concerning the interpretation of a lease agreement that stipulated rent adjustments based on a specified index, but the parties had applied a different, unwritten index for several years. The tenant sought to enforce the written index for calculating past and future rent, arguing the written clause was paramount. The court rejected the tenant's appeal, reasoning that the consistent, voluntary application of a different calculation method by both parties over an extended period demonstrated a tacit agreement to modify the initial contractual term regarding the rent adjustment mechanism, thereby validating the applied, unwritten index as the governing standard.