U.S. Daily Surface Data consists of several closely related data sets: DSI-3200, DSI-3202, DSI-3206, and DSI-3210. These are archived at the National Climatic Data Center (NCDC). U.S. Daily Surface Data is sometimes called cooperative data or COOP, named after the cooperative observers that recorded the data. In any one year there are about 8,000 stations operating. Most cooperative observers are state universities, state or federal agencies, or private individuals whose stations are managed and maintained by the National Weather Service. Each cooperative observer station may record as little as one parameter (precipitation), or several parameters. U.S. Daily Surface Data is also called Summary of the Day data. The original data was manuscript records, the earliest of which are from the 1800s. Records for approximately 23,000 stations have been archived from the beginning of record through the present. Official surface weather observation standards can be found in the Federal Meteorological Handbook.