One viewpoint is that clean floats geared to a domestic price / inflation goal stabilise exchange rates, eg Friedman (1953), much IMF advice, Dooridan and Caporale (2006). An opposite viewpoint is that managed floats (central bank intervention to maintain the exchange rate goal) reduce exchange rate volatility and crises. Our interpretation of the field data 1970 to date is that: 1) the 1980s were the hey-day of clean floats for the US vis-à-vis the future EURO countries; and 2) the managed float viewpoint is corroborated. But our interpretation rests on questionable “other things equal” and independence assumptions. We then avoid these questionable assumptions via a laboratory experiment that embeds a new theory of exchange rate determination involving the uncontroversial power of fully cooperating central banks to totally fix the exchange rate, and the role of central bank lack of full cooperation / conflict in all actual exchange rate changes. This evidence also points to managed floats being better for limiting exchange rate variations – and to transparently managed floats being superior to non-transparently managed floats. Our joint evidence suggests that the future EURO block was not forced to endure such sharp exchange rate shocks in the 1980s from the Reagan-Volcker-US Treasury combination: its own dedication to clean floats contributed to these exchange rate shocks (and thus also to the shocks for developing countries). Our model of exchange rate determination is within a broader theory that includes risk effects normally excluded, SKAT, the Stages of Knowledge Ahead Theory that we use to analyse outliers in our experimental results. Our joint field and laboratory evidence points to the wisdom of Bernanke and others in organizing in September and October 2008 currency swaps that mitigated the risk of a repetition of the exchange rate gyrations of the early 1980s under the no-swap, no exchange rate coordination clean float policy of the US Treasury of the early 1980s. Our joint evidence points further to the superiority of dollarisation, currency unions, and to merits in the Mundellian Chinese-Russian proposals for a single world money. Our joint evidence thus supports US Treasury Secretary Geithner's transient late March 2009 interest in such a single world currency evolving from the IMF's dormant powers to issue SDR, Special Drawing Rights as a widely accepted means of payment. The details of the introduction of such a single world money can moreover maintain current exchange rates, contrary to the late March 2009 market interpretation that such an SDR currency would have to entail a depreciation of the dollar.