我在自学Mankiw 的Principles of Economics 时遇到一个问,想请教一下各位经济学达人,在英文第四版的678页

Relative-Prices Variability and the Misallocation of Resources 下有这么一段话:

Suppose that the Eatabit Eatery prints a new menu with new prices every January and then leaves its prices unchanged for the rest of the year. If there is no inflation,Eatabit's relative prices—the prices of its meals compared to other prices in the economy—would be constant over the course of the year. By contrast, if the inflation rate is 12 percent per year, Eatabit’s relative prices will automatically fall by 1 percent each month

我想问的是红字"Eatabit's relative prices will automatically fall by 1 percent each month"是怎么推出来的呀.感激不尽!!