Taking the example of a 3-m-diameter rotor, there may be a mismatch between the radius of the rotor and the radius of the bearing of as much as 2 mm. The actual difference in the air gap along the 300-mm length of the bearing will be only 5 microns. The tolerance guidelines for concave air bearings have the shaft nominal-minus and the radius of the bearings nominal-plus. This helps to assure the hydrodynamic effects. When sizing radial air bearings, experience shows that the radius of the shaft being supported should be not less than the length of the curvature of the bearing and not more than five times the length of the curvature.