Method and apparatus using track scan data to qualify heads based on pes linearity

A method and apparatus to qualify heads (110) to be used in disc drives (100). The method and apparatus collect a set of track scan data (1101, 1301) by moving the head across transitions (1004, 1204) in a track on a medium. The track scan data is changed based on a difference between a writer width of the head (1001, 1201) and a nominal track width (1002, 1202) to produce modified track scan data (1401, 1501). Position error signal data (1604) is then determined from at least some of the data in the modified set of track scan data (1401, 1501). The linearity of the position error signal data (1604) is used to qualify the head (110).