A number of focused-resistivity arrays have been designed for specific applications. The vertical resolution of theses tools depends directly on the thickness of the focused current pattern. A few of these tools are shown below:

The laterolog 7 (or LL7) has a current flow lines of about 1 m.it is used in petroleum logging.

The laterolog 3 (or LL3) has a current flow lines of about 30 cm Consequently, the laterolog 3 is able " to see " formations thinner than the laterolog 7, but its depth of investigation is definitely lower. It is used in environmental and oil logging.

Laterolog 3 used at the Institute of Geophysics
(document IGL)

The Dual laterolog (or DLL) is a focused array that incorporates a deep and shallow focused array allowing several depths of investigation from a single tool.

• LLd (laterolog deep) has a depth of investigation greater than the LL7 and provides a good estimate of Rt in many case.
• LLs (laterolog shallow) utilises the same electrodes, but in a different way causing the current to diverge from the focused sheet-like pattern of the deep array, thereby reducing the depth of investigation. In this case we obtain the value closer to R_xo.