The Producer Price Index (PPI) program measures the average change over time in the selling prices received by domestic producers for their output. The prices included in the PPI are from the first commercial transaction for many products and some services.
From the BLS Handbook of Methods, chapter 14:
Known until 1978 as the Wholesale Price Index, or WPI, the PPI is one of the oldest continuous systems of statistical data published by the BLS, as well as one of the oldest economic time series compiled by the Federal Government. When it was first published in 1902, the index covered the years from 1890 through 1901. The origins of the index can be found in an 1891 U.S. Senate resolution authorizing the Senate Committee on Finance to investigate the effects of the tariff laws “upon the imports and exports, the growth, development, production, and prices of agricultural and manufactured articles at home and abroad.”
Producer Price Index-Commodities Series Id: WPUSOP3000 Not Seasonally Adjusted Group: Stage of processing Item: Finished goods Base Date: 8200
Producer Price Index-Commodities Series Id: WPSSOP3000 Seasonally Adjusted Group: Stage of processing Item: Finished goods Base Date: 8200