Updated: 2013 Nov 24 2143 UTC Data from a total of 81 real-time GPS stations from the CORS , GPS/Met, and IGS networks are used for these calculations. US-TEC provides vertical TEC and slant path values of the line-of-sight electron content to the GPS satellites in view at the time. Note that TEC values in regions outside of the CONUS have no data and should be treated with caution. This ionospheric product is designed to estimate the signal delay for single and dual frequency GPS applications.