A method of dynamically adjusting an angular speed of a light beam emitted by a scanner in measuring three-dimensional coordinates of a surface or of dynamically adjusting an acquisition rate of 3D coordinates of a surface. The magnetic pole includes a first surface exposed on an air bearing surface, a second surface facing the plasmon generator, and a third surface connecting the first surface and the second surface. An N-type impurity such as arsenic is ion implanted to a relatively low concentration in the surface of a silicon substrate in a low-voltage NMOS region thereby to form extension layers. The brake arm is pivotal between a disengaged position and an engaged position. 4 spindle after 10 minutes, ranging from 1500 mPa\xb7s to 12 000 mPa\xb7s and preferably from 2000 mPa\xb7s to 8000 mPa\xb7s.