Patent ID: 8684669

Claim:
A gas turbine engine comprising: an outer casing; an annular stationary seal structure supported within said outer casing and having an inner surface; a rotor located inwardly within said seal structure and rotatable about a rotational axis, said rotor having a plurality of blades, each said blade having a tip proximate to said inner surface of said seal structure; a measuring assembly having an outwardly facing side and an oppositely facing inwardly facing side, said outwardly facing side affixed to said inner surface of said seal structure such that said measuring assembly extends outwardly no further than said inner surface of said seal structure, said measuring assembly comprising an indicia portion that extends radially inwardly from said inner surface to a location radially inwardly from said tips of said blades, said indicia portion of said measuring assembly comprising a section that is visible on an outer surface of said measuring assembly and that is abraded by said blades during rotational movement of said rotor to provide a visual indication of a distance between said tips of said blades and said inner surface.