Guardian: Estimating BP's quarterly profits has suddenly become a finger-in-the-air affair. One factor is the tax rate, which exploded to 45% in the latest period, driven by the interplay of various currencies. The Russian angle is also confusing after last year's cash-plus-shares sale of the 50% share in TNK-BP to Rosneft, which left BP with an enlarged stake in the latter. Earnings from the 19.75% stake in the Russian energy titan are harder to read and disappointed this time. Now the truly wild element...