stable exchange rate under the classical gold standard (1)

there are four important cases to study :
1- the working of some kind of pure or modified gold standard .
2- the case of "clean" floating foreign exchange rates , available to all in either country , but fluctuating from day to day according to market demand and supply ( quite like the case of wheat , which is available to all at a price that fluctuates from day to day , depending upon competitive supply and demand ).
3- the case of controlled international trade , where each transaction requires a government license and where the foreign exchange rate may be different for different kinds of transaction , being set according to the will of the state .
4- the present-day interim " managed floating " regime still loosely related to official gold and the dollar and with its mixture of (a)some what stable and pegged rates , and (B) exchange rates floating within wide limits .