A filtration system includes a magnetic drum for removing ferrous shavings and a dual canister filter unit equipped with replaceable filter bags. The terminal receives an indicator from a base station, which indicator indicates a set of settings to use in the cell, and the settings relate to access of the radio communications network. The elevation of the sensor is given by the relationship: R1=D|)|where dt1 and dt2 are the intervals of time, determined by the sensor, taken by a pulse-echo to transit the distances R1 and R2 respectively. The liquid line is fixed so as to form a length reserve loop in the cavity.