Fig. 3From: Standardisation, calibration and correlation of the Kübler-index and the vitrinite/bituminite reflectance: an inter-laboratory and field related studyCorrelation between standards used by Martin Frey and re-measured in Frankfurt by R. Petschick (Petschick 1989). The same standards were used in Darmstadt for the present study and the correlation was nearly 1:1 (n = 25, r = 0.965). See text for regression equationBack to article page