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