Changes in commodity prices two descriptions method

The variation commodity price, usually have two characteristics commodity price changes will be described.
(1) Value Description method: direct use objects to describe price increase, rendering the price - time curve. Numerical methods described can visually describe movements in prices, but due to the large difference between the prices of various commodities, and the large amount of data, the law can not reflect the overall commodity grid change.
(2) Description growth method: Calculation same goods price growth adjacent time point, plotted growth rates of different commodities - time curve. Growth rate method described in order to calculate the growth rate during the respective adjacent commodity prices, although not directly reflect changes in price value, but can directly reflect changes in the price level.