On an GE LM2500 gas turbine powered vessel you are conducting a borescope inspection of the compressor. What is used on each compressor stage as a reference for indexing the blades?

Correct Answer: Option B — The locking lug blades.

Locking lug blades are the designated reference points for indexing compressor stages during borescope inspections. By locating these specific blades, technicians can accurately map the rotor's position, ensuring that every blade is systematically inspected for damage, erosion, or deformation in accordance with GE LM2500 technical maintenance manuals.