Please explain this diagram, i am quite lost

Fig. 6.10 The equilibrium rate of unemployment W W Equilibrium 1 relative wage Desired relative wage U un Fig. 6.10 shows the desired relative wage as a function of unemployment. The higher unemployment is, the lower is the firm's desired relative wage. If there is high unemployment, the firm is less worried about losing good workers, and hence it will set a lower wage. If unemployment falls to a low level, firms want to raise their wages so as to retain their workers