Year	% of revenue
1972	32.69230769230769
1973	32.69230769230769
1974	35.82089552238806
1975	35.95505617977528
1976	41.228070175438596
1977	41.509433962264154
1978	46.38783269961977
1979	41.37931034482759
1980	37.19332679097154
1981	41.30006565988181
1982	47.08249496981891
1983	51.71214553237024
1984	47.28909357337241
1985	55.355290920144476
1986	46.99165763094422
1987	52.19498976273636
1988	50.86848635235732
1989	54.47392985731431
1990	49.90172494719549
1991	53.1664061236591
1992	50.673847739396734
1993	48.89981164570415
1994	50.20299615366074
1995	45.60541619237675
1996	42.53315782125691
1997	42.860101409306324
1998	41.83612946958143
1999	41.713459950454165
2000	39.970083924400605
2001	40.741306743371716
2002	43.604266725551895
2003	44.525510204081634
2004	44.768662445557574
2005	40.485890173559916
2006	36.68027742967706
2007	35.885159789485016
2008	37.13074270542081
2009	39.28637649009614
2010	39.06438429272216
2011	36.15125063701367
2012	35.07096645679007
2013	35.86528215723531
2014	36.0141411401287
2015	37.86730401673107
2016	35.38559324590086
2017	35.09532825057592
2018	36.18799958306307
2019	35.29667531946023
2020	34.554626180891084
2021	36.33051966703016