Ray Optics and Optical Instrument - Lateral Shift Expansion
From below figure, Let AB is an incident ray, incident on a glass plate of thickness BM2 is the normal. The ray reflects to the path BC in the glass plate, and at point this ray emerges out CD. If we draw un deviated path of incident ray, then it goes to the path BE. If we draw a perpendicular from point C on this ray, it meets at point K.