According to research, despite an official seven-currency exchange basket, empirical evidence suggests that the rupiah was controlled by BI against the US$ alone, and indeed since the 1986 devaluation, the currency maintained near-constant purchasing power against the dollar until the 1997 crisis, the steady fall of the rupiah against the dollar essentially representing the difference between Indonesian inflation and US inflation; hence, by June 1997, the rupiah had fallen from its post-evaluation rate of Rp 1,664 to Rp 2,350, an annualised decline slightly over 3%.