Projection-diffraction symmetry [1] corresponds to the symmetry of the diffraction disks and diffuse intensity within diffraction disks of the zero-order Laue zone (ZOLZ) symmetry, which excludes the HOLZ lines in the bright field disks.

Figure 1601 shows the projection-diffraction symmetry of the [0001] CBED pattern of T1 (Al₂CuLi) crystals. The pattern symmetry is 6mm.

Note that the projection-diffraction symmetry can never be lower than the whole-pattern symmetry since the whole-pattern symmetry reflects the symmetry of the full three-dimensional (3-D) crystal.

[1] B. E Buxton, J.A. Eades, J.W. Steeds, and G.M. Rackham: Phil. Trans. Roy. Soc., vol. 281, A1301, pp. 171-94.
[2] Kenneth S. Vecchio and David B. WILLIAMS, Convergent Beam Electron Diffraction Analysis of the T1 (Al2CuLi) Phase in Al-Li-Cu Alloys, Metallurgical Transactions A, 19A, 1988-2885, (1988).