This paper explores the practical consequences of the asymptotic nature of the logarithmic wind profile in neutral, barotropic, planetary boundary layers. Recent developments in boundary-layer theory have shown that the von Kármán constant is a universal constant only in a very specific asymptotic sense; in typical atmospheric conditions its value is probably about 10% larger than the asymptotic one. Pending the development of a second-order theory, the value κ = 0.35 ± 0.02 is recommended for micrometeorological applications over smooth terrain. It is shown that K theory cannot be used in attempts to detect any trends of deviations from the logarithmic law. Abstract This paper explores the practical consequences of the asymptotic nature of the logarithmic wind profile in neutral, barotropic, planetary boundary layers. Recent developments in boundary-layer theory have shown that the von Kármán constant is a universal constant only in a very specific asymptotic sense; in typical atmospheric conditions its value is probably about 10% larger than the asymptotic one. Pending the development of a second-order theory, the value κ = 0.35 ± 0.02 is recommended for micrometeorological applications over smooth terrain. It is shown that K theory cannot be used in attempts to detect any trends of deviations from the logarithmic law.