Ideal for measuring the depth and thickness of hydrocarbon layers, the Solinst Model 122 Interface Meter uses a 5/8" probe attached to tape which is permanently marked each 1/100 ft. or millimeter, and mounted on a reel. It is powered by standard 9V batteries, which are located in easy-access drawers. The batteries give 120 hours of use and the probe has an automatic shut-off after 10 minutes.