For ∣αθ⟩=cosθ∣0⟩+sinθ∣1⟩, Alice measures her half of a Bell state in the real basis {∣αθ⟩,∣βθ⟩}, with ∣βθ⟩=−sinθ∣0⟩+cosθ∣1⟩. Bob receives one outcome bit and applies I or iY. Since iY∣βθ⟩=∣αθ⟩ for every θ, the preparation is exact and the correction is independent of the unknown parameter.