Affinograph.

Blue, green, violet and pink links create a parallelogram.

Green, brown and pink links create a right triangle.

Move yellow tracer along a given curve (a square in this case), red pen traces red curve (a rhombus in this case). It is the given curve scaled only in Y direction.

Y-scale factor: ky = P1/P2

P1: distance between end revolution joints of the pink link.

P2: distance between middle revolution joint of the pink link and end revolution joint of the blue link.

X-scale factor: kx = 1