A rotor blade assembly includes a rotor blade including one or more pockets and a housing located on the rotor blade within one or more pockets. The computer determines whether a boot-fail counter exceeds a threshold value. This pseudo-zero state is obtained by applying an index matching liquid between a first-calibration magnetic head slider, having the same optical constants as the magnetic head slider under test, and the glass disc, the index matching liquid having a refractive index identical to the glass disc.