Cl,0 ; it is how much efficient to calculate Cl,0 (i.e. Cl incompressible) when the airfoil is thin, symmetrical, at alpha = 3 degrees and moving at low speed. Actuall it appeared in my compressible aerodynamics paper where i ha to calculate CL. I was given Lift per unit span, dynamic head q, in unites of N per m. I was also given chord length. So there were two ways to calculate Cl,o. one to use thin airfoil theory Cl,o = 2 * pi * alpha. But Cl,0 can also can be calculated from L/q. So please answer what was the right way to solve it and what is basic difference in both the ways as both gave different results.