A valve includes a valve body, a valve element to selectively control flow through the valve, and a seal member and seat member together providing a fluid-tight seal between a valve cavity and a fluid passage in the valve body. The method includes providing a measured magnitude of the Fourier transform of a complex electric field temporal profile of a pulse sequence comprising a first pulse indicative of the transient response of the sample and a second pulse. The toy also includes a corresponding plurality of tethered pieces coupled to the plurality of tethers and moveable between a retracted state in which the plurality of tethers hold the tethered pieces proximate the body and an extended state in which the plurality of tethers hold the tethered pieces away from the body.