The Monroe^TM 291 uses parallel metal contact rails and jacks for connections to external electrodes or ground to measure both resistivity and resistance-to-ground. The instrument is easy-to-use, pocket-sized, and uses a twelve LED color-coded display to accurately and quickly show measured decade values.

To measure the surface resistivity of a flat sample, place the instrument on the material with the rails contacting the material and press the test button. For surface-to-ground or point-to-point measurements, make connections to one or both of the banana jacks on the end of the instrument. When a banana plug is inserted, the corresponding contact rail is disconnected.