 An Overhauser magnetometer produces readings with a 0.01 nT to 0.02 nT standard deviation while sampling once per second.The "optically pumped caesium vapour magnetometer" is a highly sensitive (300 fT/Hz0.5) and accurate device used in a wide range of applications.It is one of a number of alkali vapours (including rubidium and potassium) that are used in this way.