When determining the installment amount, it is crucial to consider a changeable benchmark. This benchmark serves as a reference point for evaluating the success of an investment or project. It is often used in the finance industry to assess the performance and viability of various financial instruments. By fixing the installment amount to a changeable benchmark, we can accurately measure the progress and profitability of our financial decisions. This allows us to make informed and strategic choices that lead to long-term financial success.