Abstract: A corrosion measuring system is disclosed which includes a sensor supportable in a fluid within a vessel, such as a pipe. The sensor is generally tubular, one end of which is closed. The closed end comprises a measuring portion having a wall of relatively medium or heavy thickness. The measuring portion adjoins a relatively thick-walled outer end hub portion having a substantial radial dimension and a relatively low or negligible resistance. A resistive element is attached to the sensing element within the sensor. In combination with electrical circuitry, the probe produces readings representative of the corrosion of the sensing element which readings are correlated to the corrosion of the vessel. Another aspect of the invention relates to a multi-range bridge circuit for use with the resistive components of the probe. Effectively, the electrical resistivity of the measuring portion and the hub portion of the sensor are precalculated to be a low percentage, e.g.