Gravity data were acquired using a LaCoste& Romberg model G (LCR G-65) relative spring gravimeter (Fig.
Calibration results of different type spring gravimeters from the repeated measurements of Estonian calibration lines.
From 1970 to 1990 four gravity campaigns were carried out on the network by using a precise USSR manufactured spring gravimeter GAG-2.
Spring gravimeters and most likely an air transport were used for the connection measurements.
It was based on the determinations of absolute gravity values with a JILAg-5 gravimeter in 1995 as well as relative gravity connections with LCR (LaCoste&Romberg) G-type spring gravimeters.
Following this, advances included the (a-stable) relative spring gravimeters
, free-fall measurements made by dropping macroscopic objects and using the methods of geometrical optics to sense motion, and finally, free-fall measurements made using optical interferometry.