Year	% of revenue
1972	2.96692607003891
1973	5.376344086021505
1974	6.546762589928059
1975	6.649367499189101
1976	5.968237704918033
2003	11.862895304123935
2004	11.54254209412704
2005	10.818609529443052
2006	10.642832765603972
2007	10.928252547516323
2008	11.219210072817074
2009	13.24865304844132
2010	13.2184072927941
2011	13.1164527084592
2012	13.662717813605374
2013	14.404306874076633
2014	12.571826767525465
2015	12.644928710025734
2020	18.37348762837258