English: Ray-tracing through a K-mirror at an angle tilted to the left by 20 degrees from its nominal zero angle.

The K-mirror is the combination of three flat mirrors with surfaces shown in purple. If viewed from the left, the three surfaces form a shape like the letter K. Three rays enter from the right, are each reflected by the three mirrors, and arrive at the green screen where their positions are recorded. The reference ray (in blue) marks the center. The brown ray starts at the right of it and arrives at the right of it on the green screen, 40 degrees upwards from the horizontal. The yellow ray starts above the blue ray and ends below the blue ray at the green screen, 40 degrees away from the vertical. The three reflections have the combined effect of flipping right-handed beams and into left-handed beams

and rotating them by twice the K-mirror rotation angle in the laboratory reference system.