Year	% of revenue
1997	10.946137985986184
1998	10.852698132342166
1999	13.264883390296491
2000	23.591686459570177
2001	19.877268910667908
2002	38.09083630496236
2003	38.92667675972723
2004	40.05672259488871
2010	35.826113489725316
2011	34.800693319768925
2012	33.615879483338034
2013	32.33613275117732
2014	32.59996257767923
2015	32.46531806950619
2016	28.7518201906014
2017	26.359258979538065
2018	30.67444174641033
2019	30.86025344697004
2020	27.932589781505403
2021	28.259998907720597