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An extension of Furnas's method is described. The variation of intensity of an axial reflection as the crystal is rotated about the goniometer axis is used to give a curve of relative transmission T against azimuthal angle φ for the corresponding reciprocal lattice level. Transmission coefficients for any general reflexion hkl are then given approximately by T(hkl) = [T(φinc) + T(φret)]/2 where φinc and φret are the azimuthal angles of the incident and reflected beams. Equations are derived for (φinc and φret and the accuracy of the method is discussed.