Year	% of revenue
1972	9.219210072088519
1973	9.718607677293448
1974	9.748121347063734
1975	11.686720142602507
1976	9.27232496973239
1977	8.769149498151071
1978	7.671806041153173
1979	7.556398015538683
1980	10.596733309192121
1981	10.658943759258321
1982	12.725875104691326
1983	11.317733267378209
1984	11.978801169590625
1985	11.628552799980673
1986	11.460426926264246
1987	12.614178484784341
1988	13.555225056703426
1989	13.978433446230873
1990	12.985722008295753