https://doi.org/10.1351/goldbook.T06342

The distance from the electrode where the ratio \[\frac{c\,-\,c_{\text{e}}}{c_{0}\,-\,c_{\text{e}}}\] reaches a given value. (ce is the interfacial concentration, c is the concentration, c0 is the value in the bulk solution.) If this ratio is selected as, say, 0.99 the corresponding thickness of the diffusion layer is denoted by δ 0.99.*See also:* diffusion layer*Source: *

PAC, 1981,*53*, 1827. 'Nomenclature for transport phenomena in electrolytic systems' on page 1837 (https://doi.org/10.1351/pac198153101827)

PAC, 1981,