1. n. [Formation Evaluation]

The resistivity measured by the buttons of a measurements-while-drilling (MWD) toroid device. Typically three buttons, each with a different depth of investigation, are mounted on a sleeve attached to the drillstring, and by their nature are azimuthally focused. The measurement is similar to a wireline microresistivity log, except that toroids are used instead of electrodes for transmitting and monitoring. The button resistivities are focused measurements with vertical resolutions and depths of investigation of a few inches. With three button measurements, it is possible to correct for the presence of invasion, assuming a step profile.

See: azimuth,  bit resistivity,  electrode resistivity,  ring resistivity