For example, iron and many other goods may rise while wheat and many other goods fall in price.

There is, therefore, no such thing as an actual _general_ change in the prices of goods in terms of money, but it may be seen that the prices of large classes of goods, often of nearly all goods, change upward or downward at the same time and in the same general direction.

We thus have need to distinguish between changes in the valuations of particular kinds of goods in terms of each other and general changes in the valuation of a number of different goods in terms of the monetary unit.
To get some idea of whether such a general trend occurs, the algebraic sum of all the changes in the particular prices of a selected group of goods may be taken, and for convenience this may be reduced to an average price (by dividing the sum by the number of articles).

Such an average is called a general price and, when comparing it with the general price of another time, we speak of changes up or down in _general prices,_ or in the _general scale of prices,_ or in the _price level._ When gold is the standard unit, its value is the converse of general prices; as prices go up the value of gold goes down, and gold is said to _depreciate_.

As prices go down, the value of gold goes up and gold is said to _appreciate_.