An electronic survey instrument for measuring distances with great accuracy. A high-frequency (3×109 Hz) radio pulse is transmitted to the ‘‘rod’’ transponder, where it is retransmitted back to the master transmitter that measures the time that has elapsed since the original transmission. Accuracy of a few inches in several miles can be achieved with proper corrections (mainly for moisture content of the air). Line-of-sight limited. Trade name of Tellurometer, Ltd.