Static track spacing error correction in a disc drive

In a disc drive having a disc with a series of many nominally concentric servo tracks, an actuator assembly adjacent the disc, and a servo system for controlling the position of a head of the actuator assembly relative to the disc, a method for correcting static track spacing errors between the servo tracks, comprising steps of:

• (a) determining a value RP indicative of an offset between a first and a second adjacent ones of the servo tracks;
• (b) determining a value RQ indicative of an offset between a third and a fourth adjacent ones of the servo tracks;
• (c) deriving {overscore (R)} as an arithmetic combination of RP and RQ, wherein {overscore (R)} is indicative of a typical adjacent-track offset for at least several of the servo tracks;
• (d) deriving a correction factor WP as an arithmetic combination of RP and {overscore (R)}, wherein WP is indicative of a static track spacing error between the first and second servo tracks;
• (e) storing the correction factor WP;
• and
• (f) using the correction factor WP during operation of the disc drive to generate a corrected position signal for use by the servo system in positioning the head with respect to the disc.