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affected by magnetic and electric fields while metal springs have a
much lower drift (elongation) with time. The test mass is sealed in an
air-tight container so that tiny changes of barometric pressure from
blowing wind and other weather do not change the buoyancy of the

test mass in air.

Figure 13.1. Gravitometer

Spring gravimeters are, in practice, relative instruments which

measure the difference in gravity between different locations.
Gravimeters have been designed to mount in vehicles, including
aircraft, ships and submarines. These special gravimeters isolate
acceleration from the movement of the vehicle and subtract it from

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