 Popular models include G-856/857, Smartmag, GSM-18, and GSM-19T.For mineral exploration, they have been superseded by Overhauser, caesium, and potassium instruments, all of which are fast-cycling, and do not require the operator to pause between readings.The "Overhauser effect magnetometer" or "Overhauser magnetometer" uses the same fundamental effect as the "proton precession magnetometer" to take measurements.