Symmetric drawing with a rhombus linkage - GIF

Symmetric drawing with a rhombus linkage.

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Previously:

1755 drawing instrument set - photos
Camera lucida drawing aid - GIF
Drawing a circle using a square - GIF
Drawing a perfect circle on a chalkboard - GIF
Drawing three right angles on a sphere - GIF
Wrist flick circle drawing technique - GIF

I have never seen the geometry of the linkage; and such a great animation to demonstrate it.

Obviously, there are people who can visualize things in their minds that most people could never imagine. This looks like a good example.