why Trade Balance reacts after a delay for exchange rate shocks?

FIGURE 7-4 Real effective 125 exchange rate (March 1973 = 100) 3% Trade balance 120 Real effective exchange rate (% of GDP) (left scale) 2 115 1 Surplus 110 Real depreciation 105 -1 Deficit 100 -2 Real 95 appreciation -3 90 -4 85 -5 Trade balance (right scale) 80 -6 75 -7 1975 1980 1985 1990 1995 2000 2005 2010