A computer implemented method of detecting a marker in a body, comprising: receiving, by a processor, an input signal from a probe, where the input signal is generated by a probe in response to detecting a marker signal from the marker; determining, by the processor, a marker proximity value based on the input signal, where the marker proximity value corresponds to a distance between the probe and the marker; generating, by the processor and for output by a user interface device, at least one feedback signal based on the marker proximity value, wherein a range of the marker proximity value is divided into a plurality, optionally between 3 and 8, of predetermined distance bands; wherein at least one parameter of the feedback signal is varied in relation to the marker proximity value; and wherein the at least one parameter of the feedback signal, or a rate of change of at least one parameter of the feedback signal in relation to the marker proximity value, is varied discontinuously at at least one boundary between two adjacent bands of the plurality of bands; wherein another parameter of the feedback signal is increased progressively in relation to the marker proximity value across more than one band of the plurality of bands and is varied continuously across more than one boundary between adjacent bands of the plurality of bands; and outputting, by the user interface device, the generated feedback signal. receiving, by a processor, an input signal from a probe, where the input signal is generated by a probe in response to detecting a marker signal from the marker; determining, by the processor, a marker proximity value based on the input signal, where the marker proximity value corresponds to a distance between the probe and the marker; generating, by the processor and for output by a user interface device, at least one feedback signal based on the marker proximity value, wherein a range of the marker proximity value is divided into a plurality, optionally between 3 and 8, of predetermined distance bands; wherein at least one parameter of the feedback signal is varied in relation to the marker proximity value; and wherein the at least one parameter of the feedback signal, or a rate of change of at least one parameter of the feedback signal in relation to the marker proximity value, is varied discontinuously at at least one boundary between two adjacent bands of the plurality of bands; wherein another parameter of the feedback signal is increased progressively in relation to the marker proximity value across more than one band of the plurality of bands and is varied continuously across more than one boundary between adjacent bands of the plurality of bands; and wherein a range of the marker proximity value is divided into a plurality, optionally between 3 and 8, of predetermined distance bands; wherein at least one parameter of the feedback signal is varied in relation to the marker proximity value; and wherein the at least one parameter of the feedback signal, or a rate of change of at least one parameter of the feedback signal in relation to the marker proximity value, is varied discontinuously at at least one boundary between two adjacent bands of the plurality of bands; wherein another parameter of the feedback signal is increased progressively in relation to the marker proximity value across more than one band of the plurality of bands and is varied continuously across more than one boundary between adjacent bands of the plurality of bands; and outputting, by the user interface device, the generated feedback signal.