Heavy quark-meson mass gap from spectroscopy
  Using a quite accurate flavour-independence of $nS$-level mass differences in heavy quarkonia and a corresponding quasiclassical expression for the heavy quark binding energy, one shows that experimental data on masses of mesons with heavy quarks allow one to make the estimate $\bar \Lambda= 0.63\pm 0.03$ GeV. 
V.V. Kiselev