Year	% of revenue
1972	22.51552795031056
1973	20.49019607843137
1974	12.60229132569558
1975	12.782608695652172
1976	14.016172506738545
1977	13.236103467253715
1978	13.704888076747373
1979	9.304964539007091
1980	8.639246588506632
1981	7.839860495531497
1982	10.362856028092079
1983	10.334601250725292
1984	9.35163426618244
1985	16.07608001179535
1986	23.28831363721628
1987	18.13889673540212
1988	24.472766522749918
1989	25.14006805760836
1990	23.7072233736036
1991	26.285512200872336
1992	25.8564517721394
1993	26.35391881813985
1994	34.027727789694936
1995	33.80465602148933
1996	30.28275869707273
1997	28.21210771745556
1998	24.974393383707838
1999	28.171760619864028
2001	25.9119693934694
2002	29.932845272339136
2003	32.14952843832401
2004	32.036356625955925
2008	27.14888423171792
2009	30.194991127126013
2010	30.632618029201776
2011	29.311672325625583
2012	32.33321873271648
2013	34.27858483353027
2014	34.0559172786579
2015	37.77237241246822
2016	35.79192223526411
2017	38.111643673493056
2018	35.89542409215084
2019	35.94079956393655
2020	38.10769130949637
2021	37.18919560976619
2022	36.97721117942241