The most common gravimeters are spring-based. Many weighing scales may be regarded as simple gravimeters. Gravity is measured using gravimeters, of which there are two kinds. Other instruments such as gravimeters and magnetometers are also used in the search for petroleum. The resolution of the gravimeters can be increased by averaging samples over longer periods. Airborne gravimeters and magnetometers can collect data from vast areas and highlight anomalous geologic features. In Atom gravimeters, the mass is a collection of atoms. When operated to report acceleration, they are useful gravimeters. Researchers use more sophisticated gravimeters when precise measurements are needed. Second, "relative gravimeters" are spring-based and are more common. The satellite borne gravimeters GOCE, GRACE, are mostly operating in gravity gradiometer mode. Gravimeters can detect vibrations and gravity changes from human activities. Thus, gravimeters can be regarded as special-purpose accelerometers.