Year	% of revenue
1972	28.11284046692607
1973	28.03970223325062
1974	28.741007194244606
1975	27.31106065520597
1976	33.40163934426229
1977	44.16020130006291
1978	43.228664997110386
1979	40.737808739708676
1980	37.1959369152633
1981	42.41770102536427
2003	6.1438298528578565
2004	5.600593003965126
2005	5.414151255241045
2006	5.050322929612292
2007	5.211740312835633
2008	4.567615691685862
2009	3.3685615063020853
2010	3.8188082135398407
2011	3.5682958809341754
2012	3.6642710518463426
2013	3.0478120879037944
2014	2.998798926131991
2015	3.310832544642337
2020	2.621651990550613