Year	% of revenue
1973	12.823152596659803
1974	9.433656957928802
1975	9.32568149210904
1976	11.417469526800447
1977	12.34499094329107
1978	10.859711271092827
1979	11.084019769357496
1980	13.156181126026848
1981	14.725691765539963
1982	15.74721330058568
1983	14.636547156275547
1984	11.856326798997246
1985	11.535640208428187
1986	10.244518498079087
1988	9.296735241502683
1989	8.990019907275745
1997	21.119649823167986
1998	22.636496969808782
1999	22.693228704573055
2000	19.029108136260717