Full of stuff like:
The MicroPhysics Fly Height tester measures the spacing between the head and disk by using a rotating transparent replica of the magnetic disk together with an actual magnetic recording head with substantially improved accuracy at very low fly heights compared to the current industry standard methods. This fly height tester does not require a spacing varying calibration and does not make use of polarized light. The technique can be performed at substantially normal incidence to the Head/Disk interface and the precision of the spot location is not compromised as it can be on a non-normal incidence system.
