Abstract: A method and apparatus of raising or lowering an oil drilling rig mounted on a platform is provided. The rig is mounted on the platform hull, which is supported by a plurality of legs. Each leg has a plurality of jacking chords. The legs are raised or lowered relative to the hull to lower or raise the rig. The elevation of each chord of a leg is measured during the raising or lowering action, and the measured elevations are used to determine the deformation of the leg. In this manner, a corrective action is instituted according to the determined deformation by acting individually on each chord of the leg.

Abstract: The invention relates to the determination of the torque T.sub.s acting at the surface in a drillstring while drilling a borehole, the drillstring being rotated by rotating driving elements which include an electrical motor with an output shaft. The method comprises the steps of: measuring the angular acceleration .gamma. of said shaft; measuring the torque T.sub.m of said motor; determining the gear ratio G; determining the moment of inertia Mt of said rotating driving elements; and determining the torque T.sub.s from the values of .gamma., T.sub.m, G and Mt.