An arbitrary state of the Hydrogen atom, ignoring spin, is labelled by | n ; ℓ, m ⟩, where the value of ℓ is a measure of the total orbital angular momentum and m is its z -component, which defines the orbit orientation. The components of the angular momentum pseudovector are L i = ε ε i j k X j P k where the products in this expression are independent of order and real, because different components of X and P commute.