APPARATUS AND METHOD FOR ALTERING TRACK SCAN DATA BASED ON HEAD WIDTH RELATIVE TO DATA TRACK WIDTH AND DETERMINING THE POSITION ERROR SIGNAL FROM THE ALTERED TRACK SCAN DATA TO QUALIFY THE HEAD IN A DATA STORAGE DEVICE

A method and apparatus to qualify heads to be used in disc drives. The method and apparatus collect a set of track scan data by moving the head across transitions in a track on a medium. The track scan data is changed based on a difference between a writer width of the head and a nominal track width to produce modified track scan data. Position error signal data is then determined from at least some of the data in the modified set of track scan data. The linearity of the position error signal data is used to qualify the head.