Year	% of revenue
1972	4.254658385093168
1973	3.6734693877551026
1974	1.3173568775839113
1975	1.6904352102286697
1976	2.284116685129504
1977	2.667700305531488
1978	3.32181922855498
1979	4.0887391182252175
1980	4.839160839160839
1981	3.729518855656697
1982	3.4984990549605306
1983	3.193266083238693
1984	3.951418629550321
1985	4.88578466106556
1986	6.860995439222685
1987	5.089200382287353
1988	5.007530120481928
1989	4.569190600522193
1990	3.182711198428291
1991	4.249582438558817
1992	3.0303030303030303
1993	0.6201550387596899
1994	0.5330834841044197
1995	0.534497349783974
1996	0.4712321668582903
1997	0.5287818921578707
1998	0.6809386175476412
1999	0.20110660450322637
2000	0.16809356430974282
2001	0.1678595236398207
2002	0.10199356117946269
2003	0.07620168007586267
2004	0.08204516707250466
2005	0.05914215665594743
2006	0.06603446685806048
2007	0.08880506480008397
2008	0.09494511431064406
2009	0.13305184588226265