In this paper we describe and demonstrate a least square method for direct measurement of the wave parameter dT/dΔ. The information necessary for doing this is the coordinates of arbitrarily spaced seismic stations and relative arrival times of the phase under investigation. The dT/dΔ parameter is derived from a function in ϕ and λ, representing the variation of T over the array. An iteration loop is included for examining and selecting a T-response function of simple form, i.e., containing few parameters, and thus making the method applicable even to arrays containing few stations. Using data from Jeffreys-Bullen tables where sometimes random errors are added, the calculated dT/dΔ values at the array centers deviate less than 0.06 from the true value and the estimates have standard errors around ±0.15.