The horizontal variometer gives the «gradient» of gravity which is defined as the rate of change of gravity over a horizontal distance of 1 centimetre. The horizontal variometer also furnishes the curvature values if the instrument is set up in the requisite number of azimuths. The gradients and curvature values are expressed in Eötvös units which are about 1*10^-12 part of the force of gravity.
In principle, the torsion balance is very simple. However, due to the extreme precision required it is a highly refined instrument. Its sensitivity can be illustrated by the following example. If a piece of metal weighing 1 gram were stretched out to encircle the Earth’s equator 25 times and 1 mm of the stretched wire were cut, the segment would weigh 1*10^-12 grams. This weight is in the order of the Magnitude of forces the Eötvös torsion balance could detect.
Eotovos’ instruments were realised in the Nándor Suess Precision Tool Workshop * predecessor of the Hungarian Optical Works (MOM). The Curvature Variometer and the Horizontal Variometer were completed in 1890 and tested in the lab and in the field in 1891. The simple gravity variometer completed in 1898 was a modified version of the horizontal variometer and was specially designed for field work. It was shown and awarded at the world exhibition in Paris in 1900.
In order to increase the efficiency of field work, Eötvös constructed a double instrument with two balances in antiparallel arrangement (1902). In later years the above-mentioned two instruments were used in experiments carried out by Eötvös and his associates to investigate the problem of proportionality of the inertial and gravitational masses.