exchange markets imposed unilaterally, 6/1000 of a basis point (or 0.00006%) is a realistic maximum magnitude." Similarly Shvedov (2004) concludes that "even making the unrealistic assumption that the rate of 0.00006% causes no reduction of trading volume, the tax on foreign currency exchange transactions would yield just $4.3 billion a year, despite an annual turnover in dozens of trillion dollars." Accordingly, one of the modern Tobin tax versions, called the Sterling Stamp Duty, sponsored by certain UK charities, has a rate of 0.005% "in order to avoid market distortions", i.e., 1/100 of what Tobin himself envisaged in 2001. Sterling Stamp Duty supporters argue that this tax rate would not adversely affect currency markets and could still raise large sums of money. The same rate of 0.005% was proposed for a currency transactions tax (CTT) in a report prepared by Rodney Schmidt for The North-South Institute (a Canadian NGO whose "research supports global efforts to [..] improve international financial systems and institutions"). Schmidt (2007) used the observed negative relationship between bid–ask spreads and transactions volume in foreign exchange markets to estimate the maximum "non-disruptive rate" of a currency transaction tax. A CTT tax rate designed with a pragmatic goal of raising revenue for various development projects, rather than to fulfill Tobin's original goals (of "slowing the flow of capital across borders" and "preventing or managing exchange rate crises"), should avoid altering the existing "fundamental market behavior", and thus, according to Schmidt, must not exceed 0.00005, i.e., the observed levels of currency transaction costs (bid-ask spreads). The mathematician Paul Wilmott has pointed out that while perhaps some trading ought to be discouraged, trading for the hedging of derivatives is generally considered a good thing in that it can reduce risk, and this should not be punished. He estimates that any financial tax should be at most one basis point so as to have negligible effect on hedging. Assuming that all currency market participants incur the same maximum level of transaction costs (the full cost of the bid-ask spread), as opposed to earning them in their capacity of market makers, and assuming that no untaxed substitutes exist for spot currency markets transactions (such as currency futures and currency exchange-traded funds), Schmidt (2007) finds that a CTT rate of 0.00005 would be nearly volume-neutral, reducing foreign exchange transaction volumes by only 14%. Such volume-neutral CTT tax would raise relatively little revenue though, estimated at