2. . 
The distance between the external surface of a logging tool and the borehole wall. This distance has an important effect on the response of some logging measurements, notably induction and neutron porosity logs. For resistivity tools, the effect of standoff is taken into account in the borehole correction. In the neutron porosity tool, it is usually corrected for separately. In a smooth, regular hole, the standoff is constant and determined by the geometry of the logging tool string and the borehole. In rugose or irregular holes, standoff varies with depth.