$21\mathrm{.}1$ J$-$A US Five$-$Dollar note printed in $1961$ is worth exactly dollars today. In $1961,$ one US dollar bought. joods and$/$or services than that same exact dollar buys today. The amount of goods and$/$or services that a currency can buy is referred to as its $..$power. Over time. $.$ is the phenomenon most often attributed to the erosion of this power.