The sign will depend on the specific definitions of the variables X and Y. An example would be X = volume and Y = pressure. Additionally, the variance in X will be ⟨ ⟨ ( Δ Δ X ) 2 ⟩ ⟩ ≡ ≡ ⟨ ⟨ ( X − − ⟨ ⟨ X ⟩ ⟩ ) 2 ⟩ ⟩ = ∂ ∂ ⟨ ⟨ X ⟩ ⟩ ∂ ∂ β β Y = ∂ ∂ 2 ln ⁡ ⁡ Z ∂ ∂ ( β β Y ) 2 .