Astigmatism(axial): an electron-optical lens aberration that causes the defocus to be a function of azimuth, and the contrast transfer function to deviate from circular symmetry about the optical axis. As a consequence, the Thon rings deform into elliptic or hyperbolic patterns, depending on the size of defocus and the size of the astigmatic defocus difference. A flag for Y or N for astigmatism estimation