The most accurate measures of the acceleration of gravity are got nowadays by using the gravimetres which are extremely sensitve spring balances beased on the measuratrion of the weight of a constant mass. The value of the mass is known so by measuring its weight it is easy to find the value of the acceleration of gravity (P=mg).
The most precise gravimetres reach a precision of the order of 10-8 m/s2, but it took a century of work to obtain this result and an amount of research aimed at improve the official value fixed in 1909 at the General Conference in London, whose precision was of the order of 10-6 m/s2. A report written in july 2003 by CNR pointed out, among the factors responsible for this improvement, the great collaboration between international bodies specialized in geodetic and geophysics and the universities together with the development of the information technology. The 20th century saw the use, for the first time, of underwater gravimetres activated by a remote controls with which it was possible to draw a more accurate map of the gravimetrical net than anytime before (a complete map of the Mediterranean Sea was drawn just after the second world war). Other benefits to the evolution of the gravimetres were apported by the development of the studies on terrestrial stratums, on the chemycal reactions which takes place there and on the tectonic movements.
The precision reached nowadays let us improve the studies on meteorology geophysics, geology, vulcanology and the possibility of finding deposits beneth the surface, controlling the eruptions, the earthquake and the level of the seas. Also everyday life gets great benefits from an accurate evaluation of the acceleration of gravity on which depend, for example, the calibration of weighing tools and the orbits of satellites.