I would like to ask exactly what it means when a currency cross has a historical volatility of, say, 10%. I understand that the 10% is the volatility expressed in annual terms, and that it represents a one standard deviation move. Also, I understand that one standard deviation represents two thirds (approximately) of all occurences, but - but then my question is - what does that mean exactly? Will it mean that Currency cross X, at the beginning of the year is trading at 100, will, in two thirds of the cases, stay between 90 and 110? Or will it, in two thirds of the cases, stay between 95 and 105? Or none of the above? This is basically my doubt.