Brown bar pivots in the vertical plan.
Red tracer of the brown bar moves on yellow sample and blue spherical milling cutter creates 3D surface on the pink work.
Length of blue bars: a + b. Here b = a
Length of green bars: a
Length of violet bars: b
Reducing copy ratio: i = a/(a+b) = 1/2
Length of orange bar: x
Length of pink bar: y
Distance between two fixed pivots of the blue bars: z
Condition to get orange and pink bars translate: (y-x)/(z-x) = b/(a+b) + 1/2
Length of brown bar: e + f
Condition to get right reducing copy ratio i in vertical direction:
e/(e+f) = a/(a+b) = 1/2
Because the tracer does not move exactly vertically so there is some error for the created surface.