Abstract: A system for determining the position and/or orientation of electromagnetic receivers in a network of receiver instruments at a remote location, a first receiver instrument including one or more electromagnetic sensors, the system comprising transmitting means to send a characteristic signal, detecting means to detect transmitted signals from a plurality of receiver instruments, depth measurement means to measure the depth of the first instrument, recording means to store data from the transmitting means, the detecting means and the depth measurement means, and processing means for processing data from the receiver instruments.