The operation of propagation self servowrite can be improved by using spirals written upon the disk. The spirals can be used to reduce the DC drift of the propagation of the self servowrite. The writing of the spirals can be improved by using the back EMF signal for the VCM to control the velocity of the actuator during the writing of the spirals to produce a more consistent spiral shape. Additionally, back EMF crossings of the spindle can be used to space the spirals evenly about the disk.

 
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> Circuits, systems, and methods for capacitive fly height measurement

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