Patent ID: 7911723

Claim:
An offset amount measuring method for measuring an offset amount between a write head and a read head of a composite magnetic head, comprising the steps of writing a test data obliquely in a designated track and at least one track adjacent to the designated track of one of a rotating magnetic recording medium of a discrete track system, a rotating magnetic recording medium of a bit patterned system and a rotating magnetic recording medium having an unevenly patterned recording layer by moving the composite magnetic head positioned in the designated track under ON track servo control in which a servo information is read out from the designated track, at a designated moving speed K in a radial direction of according to a write start signal by crossing the designated track, reading the test data by the read head by positioning the composite magnetic head in the adjacent track under the ON track servo control, detecting a peak position in a read signal read out by the read head, obtaining a scan time of the read head from a starting time of the write start signal to the peak position of the read signal, obtaining a relative moving distance in the radial direction of the read head with respect to the test data written in an area from a write start position to the peak position of the read signal by multiplying the scan time with the designated moving speed K, and calculating the offset amount between the heads with using a difference between the relative moving distance and a distance between the designated track and the adjacent tracks.