Year	% of revenue
1972	20.41904761904762
1973	22.411444141689373
1974	22.48330447687361
1975	24.697720515361745
1976	23.6561153774115
1977	25.134792261338408
1978	24.621838057709418
1979	24.64469944204653
1980	24.17514374170721
1981	25.365634140853523
1982	27.136648961854178
1983	31.299233840509334
1984	28.341286170818194
1985	28.125402067161296
1986	25.213159755438173
1987	24.607267534116154
1988	26.490210297316896
1989	26.606072452436802
1990	27.471620227038184
1991	28.135930612825256
1992	28.85390951531298
1993	27.579683048433047
1994	26.66839367913437
1995	27.642638571483907
1996	25.501266357112705
1997	14.311718980615959
1998	13.380333951762523
1999	11.970422282616193
2000	10.650176949317117
2001	10.248516277055264
2002	8.727609840082112
2003	7.598580565470894
2004	7.25611990972048
2005	6.670356792856884
2006	6.247527363840169
2007	6.1214201516825195
2008	5.913606196723924
2009	5.811186569451094
2010	6.225297250180461
2011	5.051997579544335
2012	5.871888471547651