DLL. A formation resistivity log made from a system consisting of both very deep and shallow investigative laterolog schemes. The tool records, in combination, deep and shallow laterolog curves and a gamma ray and/or SP curve. The dual laterolog-R_xo, is a simultaneously recorded dual laterolog which also includes flushed zone resistivity information derived from a micro-Spherically Focused Logging device. See also laterolog. DLL is a mark of Schlumberger.