where F φ here is the field needed to reduce to zero a Schottky–Nordheim barrier of unreduced height equal to the local work-function φ, and f is the scaled barrier field for a Schottky–Nordheim barrier of unreduced height φ. [This quantity f could have been written more exactly as f φ, but it makes this Fowler–Nordheim-type equation look less cluttered if the convention is adopted that simple f means the quantity denoted by f φ in, eq. (2.16).] For the example case (φ = 4.5 eV, F = 5 V/nm), f ≈ 0.36 and v (f) ≈ 0.58; practical ranges for these parameters are discussed further in.