Year	% of revenue
1973	32.54593175853018
1974	34.487877288471054
1975	34.35476909797151
1976	53.79209370424597
1977	52.48275862068965
1978	45.09098180363927
1979	41.97571927490437
1980	39.64470088065594
1981	37.5743162901308
1982	36.254783360079
1983	38.67959716523685
1984	38.499324573253105
1985	37.09166260360799
1986	36.6082762122366
1987	36.93635660912136
1988	26.270063319098806
1989	30.204122877930477
1990	27.547075695223842
1991	32.00136031287196
1992	32.676070579907986
1993	31.056531387520213
1994	28.67321635958442
1995	25.858298153705306
1996	25.81967213114754
1997	29.050151541144853
1998	26.39064122700861
1999	27.460233513689435
2000	32.83938850126217
2001	27.997834299285074
2002	22.077694298385335
2003	19.2875473033819
2004	23.256874877652287
2005	30.72734017136568
2012	11.200856859228168
2013	13.458143788493912
2014	12.172856838715365
2015	15.27650029302757
2016	23.852117503377265
2017	19.65768112975215
2018	23.733044925661964
2019	24.406335412877077