Sensor time-varying properties. Each of several sensors is placed on a calibration tube for at least 30 seconds, and then stretched flat on a table in order to verify that a constant relationship exists between bend angle and measured resistance. Ideally, these curves should be flat but a significant time-varying decay renders most unusable for this application. This figure shows several representative curves for the three manufacturers evaluated. AG: Abrams-Gentile sensors, SS: SpectraSymbol sensors, FP: Flexpoint sensors (several types).