Compressional sound velocity as a function of density as derived from pulsed-laser techniques. Violet crossed diamonds (Crowhurst et al., 2004); orange lined diamond (Chigarev et al., 2008); blue open diamonds (Decremps et al., 2014). Lines are linear fits to the experimental data sets. The star is the ultrasonic determination reported in Mao et al., (1998). PREM is shown as crosses.