Year	% of revenue
1972	31.80952380952381
1973	31.84604904632153
1974	27.009646302250808
1975	26.08523290386521
1976	28.43229069114066
1977	30.4313352362829
1978	27.90136011185967
1979	25.58164017264975
1980	23.485183547103052
1981	25.16312907822695
1982	22.766779333655236
1983	23.351677997194344
1984	21.54270454843935
1985	21.537933696444654
1986	23.553633074075613
1987	23.85353855918756
1988	22.733865119651924
1989	20.79424029189471
1990	20.905204186937933
1991	24.31679226503626
1992	22.56006648253611
1993	22.20664173789174
1994	21.080844110555365
1995	21.175969322539412
1996	20.72428591529478
1997	34.02374626914625
1998	35.38701298701299
1999	37.95025314884048
2000	38.55834217015242
2001	38.44217870228382
2002	37.21374256420444
2003	36.522176047565715
2004	36.991454310461236
2005	36.29087873398425
2006	35.03643017275485
2007	33.96472602993617
2008	32.40227229552098
2009	33.14482870297799
2010	32.79027007885812
2011	28.721333314570114
2012	30.50695951985698