Table 5 provides a list of common standard values for calibration. The calibration sphere TS is dependent on the water temperature and salinity (i.e., sound speed dependent). The copper spheres specified for each frequency have been shown to be “optimal” in that the TS of the specified spheres vary minimally for a normal range of temperatures and salinities (Foote et al. 1987). However, many groups use a single tungsten carbide sphere to calibrate multiple frequencies (Foote 1990).