Alternative exchange rate systems represent attempts to improve upon the economic efficiency of conventional exchange rate systems by combining or modifying their operating characteristics. The crawling peg or gliding parity is an attempt to combine the advantages of fixed exchange rates with the flexibility of floating exchange rates. The net effects of crawling peg adjustments might be expected to be similar to those of fixed and floating exchange rates, but without the former's economic dislocation and the latter's exchange rate volatility. The exchange rate system referred to as the Snake in the Tunnel is essentially of historical interest, having been introduced in April 1972 and abandoned in March 1973. The essence of the european monetary system is a system of fixed but adjustable exchange rates. Its operation is technically complex and consists of two elements: a grid system and a currency basket.