Had it explained to me like this once.
A 125 years ago(more or less) a US $20 gold piece would buy a very, very nice suit of clothes. Today that same $20 gold piece will buy you a very, very nice suit of clothes.
A 125 years ago(more or less) a US $20 gold piece would buy a very, very nice suit of clothes. Today that same $20 gold piece will buy you a very, very nice suit of clothes.