A rate-jump method can be used to return an intrinsic elastic modulus of the sample that is independent of the test conditions. In this method, a constitutive law comprising any network of (in general) non-linear dashpots and linear elastic springs is assumed to hold within a very short time window about the time instant tc at which a sudden step change in the loading rate is applied on the sample. Since the dashpots are described by relations of the form formula_82"ij"=formula_82"ij"(formula_62"kl") but stress formula_62"kl" is continuous across the step change ∆formula_86"ij" in the stress rate field formula_86"kl" at "t"c, there will not be any corresponding change in the strain rate field formula_82"ij" across the dashpots. However, because the linear elastic springs are described by relations of the form formula_89"ij"="S""ikjl"formula_62"kl" where "S""ikjl" are elastic compliances, a step change ∆formula_82"ij" across the springs will result according to