The name given to a series of well-[[survey|surveying]] operations in open holes, for the determination of borehole and geophysical data, by C. and M. Schlumberger and E. G. Leonardon in 1932. The survey measurements made in this early well-logging program were:

(1) [[Resistivity]] of the rocks. By a [[lateral device]].

(2) Delineation of [[porosity]] in rocks by [[electrokinetic potential|electrofiltration potential]] measurements made with an [[SP]] electrode.

(3) Electrical [[anisotropy]] of the rocks. Determination of the direction of [[dip]] by an early form of [[dipmeter]].

(4) Temperature measurements.

(5) Resistivity of the [[mud]]. Location of water flows.

(6) The electromagnetic teleclinometer. Survey of crooked holes.