More than 11,000 volunteers and contractors use instruments provided by the National Weather Service (NWS) to record daily measurements of maximum and minimum temperature, liquid precipitation, and snowfall. Some observers also provide additional information such as snow depth, soil temperatures and evaporation, along with other special phenomena including the number of days with thunder or hail. Established in 1890, the COOP network is the oldest and largest official monitoring network in the U.S. Observations are usually taken only once per day and are generally not available in real time. No formal training or certification examinations are required of volunteers.