Wiktionary
n. (context physics English) Any of several instruments used to measure the gradient of a physical property (such as magnetic field)
Wikipedia
A gradiometer measures the gradient (numerical rate of change) of a physical quantity, such as a magnetic field or gravity.
Usage examples of "gradiometer".
Instrument used by Gunn aboard the Prosperteer to approximate the length of the object he detects with the Schonstedt Gradiometer.
Armed with enough data to inspire an attempt to find Carondelet, Walt Schob and I flew to Cincinnati, Ohio, along with our Schonstedt gradiometer.
Wanting to confirm that the dredge had indeed pulverized the hull of Carondelet, Walt and I set up our search grid with buoys and dragged the gradiometer from one end to the other, finishing up just before duk.
We walked grids with the Schonstedt gradiometer under and around the modern steel-girder bridge (built in 1935) that spans the creek over the exact spot as the one that was washed away in 1878.
Equipment included a Schonstedt gradiometer to detect the presence of iron, a Klein & Associates side scan sonar to record objects protruding from the sea bottom, and a Loran navigation unit, since made obsolete by newer Global Positioning Systems, utilizing satellites.
Gradiometers for detecting iron, side-scan sonar and sub-bottom profiler to sweep the sea floor, everything for an underwater search expedition.