When test responses from specimens such as Post-Mortem Human Surrogates (PMHS), anthropomorphic test devices (ATD) or vehicle crash events are “perfectly repeatable,” the response in terms of transducer time histories is similar and the output from any one of the tests can be used to represent any other test. However, if there is test-to-test variability, the underlying fundamental response as obtained by the transducer time history is not determined by a single test and methods are needed that can use multiple tests to reduce the inherent error. This paper will explore, using different transducer time histories from PMHS, ATD and vehicle tests, the effect of signal alignment and signal “shape” on the results from signal addition. New procedures for transducer time history alignment and signal addition will be introduced and discussed, and different methods of obtaining the underlying response will be evaluated.