Year	% of revenue
1972	9.868421052631579
1973	13.976945244956774
1974	54.25844346549192
1977	93.74372699899632
1978	89.35960591133005
1979	95.9099643151249
1980	96.97802197802197
1981	95.88198169769643
1982	94.99063670411985
1983	95.24728588661037
1984	95.38779256539696
1985	96.70532419609911
1986	97.70236087689713
1990	97.36842105263158
1991	96.94656488549617
1992	99.14529914529915
1993	96.51521835024262
1994	95.87426326129666
1995	96.88546550569323
1996	97.27136431784108
1997	97.42181904989258
1998	96.58959537572255