The residual displacement is the displacement at the end of the response when the SDOF system comes to a stop, hence it generally corresponds to the last displacement value over the response duration for damped systems. Bispec computes the response for a certain duration beyond the end of the record, in order to allow the fluctuations in the residual displacement to damp out to very small values. For undamped or lightly damped systems, the displacement response may oscillate for a long time or indefinitely. In such situations, Bispec will estimate the residual displacement from the average of the last several peaks and valleys in the response.