A unit of magnetic flux density equal to 10-9 tesla (1 nanotesla) or 10-5 oersted (10 µOe). In geophysics, small changes in the Earth's magnetic field are traditionally stated in gammas. The nanotesla (nT) is now recommended for these measurements
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}