# Moment Coefficient Variation with Angle of Attack

looking at the moment coefficient for certain NACA profiles, I noticed that their graph changes with AoA and is not a constant horizontal line as I would expect (pure moment independent of the AoA). This seems to imply that the moment and the associated moment coefficient is measured relative to a point $$P$$ (maybe the leading edge $$LE$$?) that is not the aerodynamic center $$AC$$ (otherwise the moment would be independent of Aoa) but I am not sure what that reference point may be. The figure below illustrates what I discussing...