1. Horizontal, e.g., a lateral velocity gradient means change of velocity in the horizontal direction, lateral resolution means the horizontal (spatial) resolution. 2. A type of resistivity log, now little used. A constant current passed between electrode A in the borehole and a remote electrode while the potential difference was measured across two electrodes, M and N, located on the sonde; see Figure E-10. The MN distance was small compared to the spacing, the distance between the current electrode and the midpoint between the potential electrodes, often 18 ft 8 inches (5.69 m). A short lateral sometimes used a spacing of 6 to 9 ft (1.8 to 2.7 m). The potential electrodes were usually below the current electrode, but on a reciprocal sonde the functions were interchanged. 3. A horizontal well; see multilateral.