Year	% of revenue
1972	25.482330468003862
1973	19.05156690432771
1974	33.62238219895283
1975	42.06824304100571
1976	41.91867852604827
1977	41.332458770614565
1978	30.756332186038414
1979	26.006735978913436
1980	25.514024074180774
1981	21.6907784666864
1982	25.064435544629042
1983	22.58366244024111
1984	20.222629116168143
1985	20.055917508849404
1986	20.43386491557219
1987	19.874508782214058
1988	18.836792593698732
1989	19.254127918011022
1990	19.617811074184615
1991	21.01274210693433
1992	20.47578200949276
1993	20.037118850929552
1994	18.64150481618097