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measurements of absolute gravity at a number of sites in Europe and
the United States since 1976. A French group, in 1977, advertised its
plans to manufacture a version of the Italian apparatus for sale.
As absolute equipment continues to be miniaturized and made

more portable, absolute gravity measurements are becoming more
commonplace.
Before the 21st century, the measurement of gravity force

requires much effort but the rate of success is not large. The main
reasons are the requirement of measurement of the line length and the
period at the same time. Especially, there are difficulties to measure
the length of the line. It is difficult to achieve the required precision.

With the use of laser and superconductivity technology to improve the
instrument, the nGal class precision absolute gravity instrument, may
achieve the high precision absolute gravity measurement.

Relative measurement of gravity-Solution of some of the
problems of gravimetric geodesy requires knowledge of the
acceleration of gravity at very many points distributed uniformly over

the entire surface of the Earth. Since absolute gravity measurements
have been too complicated and time consuming and, until recently,
could not be obtained with sufficient accuracy, relative gravity

measurements have been used to establish the dense network of
gravity measurements needed. The earliest relative gravity
measurements were made with reversible pendulums. Since the theory
of relative pendulum measurements is somewhat simpler than that of

absolute pendulum measurements, better accuracy was obtained for
the former. However, the equipment was bulky, measurements were
time consuming, and better accuracy was desired than could be

obtained with pendulums. The most accurate relative pendulums to be
developed were the Gulf quartz pendulum and the Cambridge invar
pendulum. These two instruments were used as late as 1969.
Modern relative gravity measurements are made with small, very

portable, and easily used instruments known as gravimeters (gravity
meters). Using gravimeters, highly accurate relative measurements
can be made at a given site, known as a gravity station, in half-an-hour

or less. Modern gravimeter-type instuments were first developed in
the 1930's. Although at least 28 different kinds of gravimeters have
been developed, only two types have been used extensively. The

LaCoste-Romberg gravimeters are used for most geodetic work today,

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