from gow curve, measure tau, delta and omega, i'e. T2-T1=omega; T2-Tm=delta and Tm-T1=tau. get delta/omega. Tm for maximum intensity, Im and T1 and T2 for Im/2; so if the ratio of delta/omega is 0.38-0.42, then 1st order, or 0.48-0.52 then second order and from >0.42 to