This Technical Specification describes means to allow "attenuated" acoustic quantities to be calculated under conditions where the associated acoustic measurements, made in water using standard procedures, may be accompanied by significant finite-amplitude effects. This Technical Specification establishes: - the general concept of the limits of applicability of acoustic measurements in water resulting from finite-amplitude acoustic effects, - a method to ensure that measurements are made under quasi-linear conditions in order to minimise finite-amplitude effects, - the definition of an acoustic quantity appropriate for establishing quasi-linear conditions, - a threshold value for the acoustic quantity as an upper limit for quasi-linear conditions, - a method for the estimation of attenuated acoustic quantities under conditions of nonlinear propagation in water.