Real and nominal measures

Output, Expenditure and Income can be valued at current market price in which case we speak, for example, of money or Nominal NNP, or NNP valued at current prices.  Changes from one year to another are then a compound of changes in physical quantities and prices.  Output, Expenditure and Income can also be valued at the prices ruling in some base year.  In this case, each year's quantity is priced at its base-year prices and then summed.  We then speak, for example, of GDP at constant prices, or REAL GDP.  Changes in constant-price GDP give a measure of real or quantity changes in total output.