Abstract: A measuring device for long-term installation in a bore in a rock formation or detecting gradual changes in bore diameter, especially gradual constriction which might affect the condition of radioactive waste deposited in the bore, utilizes telescoping parts under outward spring pressure. One of the two elements of the transducer which by the relative displacement of these elements measures changes in diameter, is a rod held in a friction mounting on one of the telescoping parts that maintains the position of the device in the bore. The other element of the transducer is fixed on the other telescoping part which also carries limit stops (7,8) which in corporation with a stop (6) on the rod confines the lengthwise movement of the rod to a stroke equal to the maximum measuring range of the transducer. For measuring gradual constriction, the transducer is automatically set to begin with the maximum measureable diameter.