Year	% of revenue
1973	33.893845801876
1974	32.57281553398058
1975	34.59725353556057
1976	34.635652312769466
1977	33.67702382611119
1978	33.33714242181846
1979	32.70840197693575
1980	32.09777599679423
1981	31.36559834852055
1982	31.74381258265634
1983	31.275129715210465
1984	34.07717913944027
1985	31.899124803966206
1986	31.81712053997835
1988	31.240416560184002
1989	32.56261532661821
1997	29.263811504100058
1998	27.082391683347325
1999	28.928100746815055
2000	30.299969611323558