Toothed gears 1 and 2 rotate in opposite directions about fixed axes A and B. Taking the sign of the angular velocities ω₁ and ω₂ of gears 1 and 2 into account , the transmission ratio of the mechanism is i₁₂=ω₁/ω₂=-r₂/r₁=-z₂/z₁ where r₁ and r₂ are the pitch radii, and z₁ and z₂ are the numbers of teeth of gears 1 and 2.
$2301$SG,3L$