After the devastation wrought by what is now officially known as the 'Great Tohoku Kanto Earthquake', Japan's currency rose in value. It's the last thing Japan's under-pressure economy needs - the high yen has been a serious bugbear for Japanese multi-nationals for some time. It seems a little counter-intuitive for the currency to be rising in value at this time, given the hit the Japanese economy will be taking. Share prices on the Tokyo Stock Exchange duly tumbled, so what's going on with the currency, asks Dave Leggett.