Changes in the value of money can be measured by a price index. A price index is a measure of the average price of a basket of goods and services consumed in an economy. The price index is used to track the changes in the price of goods and services over a period of time. The most commonly used price index is the Consumer Price Index (CPI), which measures the price changes of a basket of goods and services purchased by households. The CPI is used by the government and central banks to monitor inflation, which is the rate at which the prices of goods and services are increasing over time. By monitoring inflation, the government can adjust policies and take necessary actions to stabilize the economy.