Science and engineering in Manchester chemist visited Manchester in the 1840s. In his research in Manchester, Smith discovered the existence of acid rain, a by product of the industrial revolution. Smith consequently pushed for greater environmental awareness and helped to found the Noxious Vapours Abatement Society in Manchester, which raised awareness of the consequences of poor air. Joseph Whitworth was an engineer and inventor who hailed from Stockport, Cheshire (now Greater Manchester). A talented mechanic amongst various other engineering roles, for long periods of his life, he worked in factories in Manchester. Whitworth would ultimately devise a standard screw thread system, the first of its
Precision and recall of documents, precision is the number of correct results divided by the number of all returned results. Precision takes all retrieved documents into account, but it can also be evaluated at a given cut-off rank, considering only the topmost results returned by the system. This measure is called "precision at n" or "P@n". Precision is used with recall, the percent of "all" relevant documents that is returned by the search. The two measures are sometimes used together in the F1 Score (or f-measure) to provide a single measurement for a system. Note that the meaning and usage of "precision" in