As they approached the airport they would tune in the signal and listen to it in their headphones. They would hear dots or dashes if they were to the side of the runway, or if they were properly aligned, the two mixed together to produce a steady tone, the equisignal. The accuracy of this measurement was highly dependant on the skill of the operator, listening to the signal on earphones in a noisy aircraft whilst often communicating with the tower at the same time.[1]