sliding scale
noun [ C usually singular ] uk/ˌslaɪ.dɪŋ ˈskeɪl/ us/ˌslaɪ.dɪŋ ˈskeɪl/
滑动折算制，浮动计算法
a system in which the rate at which something is paid changes as a result of other conditions
Charges are made on a sliding scale, which means that the amount you must pay increases with the level of your income. 费用按浮动费率缴纳，这意味着你必须缴纳的金额会随着收入水平的提高而增加。