Patent ID: 8878526

Claim:
A magnetic scale for magnetic encoder apparatus, comprising: a scale member comprising a plurality of grooves, the scale member defining a passive magnetic scale track that can be read by an associated magnetic scale reader unit that comprises a magnet and a plurality of magnetic field strength sensors, the passive magnetic scale track having local magnetic permeability variations that affect the magnetic field generated by the magnet of the associated magnetic scale reader unit, the plurality of grooves comprising grooves of at least a first groove type and a second groove type, the magnetic properties of the scale member in the locality of grooves of the first groove type being different than the magnetic properties of the scale member in the locality of grooves of the second groove type, wherein the scale member carries absolute position information in the form of at least one codeword comprising a sequence of data bits, wherein each of the data bits is provided by a groove of the scale member, the data bit taking a first value if the groove is of the first groove type and a second value if the groove is of the second groove type, wherein the midpoints of the plurality of grooves are substantially equidistantly spaced apart along the length of the scale member.