A magnetic marker for use in locating tissue for surgery includes a casing and two to five magnetic elements arranged in a row. The two or more magnetic elements are separated from each other by an isolating material. The magnetic marker may be non-bio-absorbable. This means that the magnetic marker is invariable as it does not decay over time. This invariability ensures that on the basis of the signal measured by a magnetometer device a distance between a probe of the magnetometer device and the magnetic marker can be determined.