Abstract: A magnetic field emitter (100) for emitting a magnetic field into an environment having a rotatable magnetic member (102) comprising one or more magnetic dipoles; a support (104) for the rotatable magnetic member (102), wherein the support (104) is configured to be placed in a support position on a surface of the environment such that when the support (104) is in the support position the one or more magnetic dipoles of the rotatable magnetic member (102) lie in a substantially horizontal plane; and a rotation mechanism (106) operable to rotate the rotatable magnetic member (102) relative to the support (104) about a rotation axis, such that when the support (104) is placed in the support position on the surface, the rotation axis is substantially orthogonal to said substantially horizontal plane such that the substantially horizontal plane remains substantially horizontal during the rotation.