A method is disclosed for identifying wedge time shift zones on a magnetic
disk of a disk drive. The disk drive further includes a spindle motor for
rotating the disk at an operating speed in response to a spindle control
current generated by a spindle control system, and a head that is
actuated over the disk. During operation, the control systems causes a
seek of the head across the disk and measures wedge-to-wedge times
between servo wedges. The control system then calculates a wedge-to-wedge
time shift value using the wedge-to-wedge times and determines whether
the wedge-to-wedge time shift time value exceeds a predetermined
threshold. If the wedge-to-wedge time shift value exceeds the
predetermined threshold, then the control system identifies a wedge time
shift zone, and stores information for compensating for the identified
wedge time shift zone during disk operations.