Year	% of revenue
1972	32.758620689655174
1973	36.76470588235294
1974	40
1975	43.28358208955223
1976	38.82352941176471
1977	38.17427385892116
1978	35.714285714285715
1979	35.99088838268793
1980	50.37147102526003
1981	53.203661327231124
1982	57.30411686586986
1983	73.32657200811359
1984	72.34179939733104
1985	71.74807903402855
1986	64.44977716832362
1987	67.38647700576063
1988	61.63993749485977
1989	55.897252861123256
1990	56.048554403001546
1991	54.595956379282285
1992	49.608963017180265
1993	48.5617832285496
1994	47.88959280280728
1995	54.2998548332005
1996	56.941264621404486
1997	59.59786445671719
1998	58.832898552749505
1999	57.82066911965328
2000	62.128000789519135
2008	21.79071729874153
2009	24.621007454152245
2010	25.53096520248625
2011	23.02997622268284
2012	22.984717283306747
2013	21.409641047094123
2014	25.40978655583312
2015	30.168886387261708
2016	30.395533376394358
2017	27.245102939095865
2018	29.061421072638034
2019	30.340080614512328
2020	32.57196879291615
2021	31.538267716640323
2022	26.304904172204914