An instrument that provides a simple means for testing electric blasting circuits, enabling the blaster to locate breaks, short circuits, or faulty connections before an attempt is made to fire the shot. With its use, misfires may be prevented to a great extent. To test a circuit, one wire should be placed on one terminal of the instrument and the other wire on the other terminal. If the needle is not deflected, it indicates that the circuit is broken; if it is an electric blasting cap that is being tested, this should be discarded.