A method of calculating wave amplitudes by ray tracing is presented. It consists of an integration of six first‐order differential equations, and three second‐order quasilinear differential equations. The six first‐order equations are the ray equations, and an equation for an additional Euler angle ψ. Two of the second‐order equations are equations for two scale factors,h2andh3, of an oblique system a2, a3defined on the wavefront. The third second‐order equation determines the angle χ between a2and a3.