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2. The Optically Variable Device (OVD) as an Anti-Counterfeiting Feature;Lee,1998
3. G. Antes, “Optically variable surface patterns”, European patent EP 375 833.
4. R. A. Lee et al, “Diffraction Grating”, European Patent no. EP 0449 893 B1.
5. R. A. Lee, “Diffraction Grating and Method of Manufacture” European Patent No. EP 0 490 923 B1.