Year	% of revenue
1973	2.645721372467962
1974	2.1074502819827843
1975	1.7564870259481038
1976	1.348148148148148
1977	0.7468688957830633
1978	1.0239651416122004
1979	1.923385157877865
1980	2.3542194856935894
1989	6.490184794424196
1990	7.344476994657935
1991	10.800744878957168
1992	12.146056327336217
2014	2.870421180436021
2015	2.878498841864026
2016	3.249265831756603
2017	3.881773049566094
2018	4.458963321802196
2019	4.407724503371906
2020	5.523925452012462