How does Mt.Gox calculate high and low price? How does Mt.Gox. calculate high and low price? How can last price, over time, be higher than the high price?
The High Price is the lowest sell order that is on the exchange. Conversely, the Low Price is the highest buy order on the exchange. 

However, the Last Price is calculated differently. It looks at what the price was the last several times that bitcoins changed hands.

If Last Price is higher than High Price, or lower than Low Price, that is indicative of one of two things:


Someone is trying to manipulate the last price by trading bitcoins absurdly high or low.
The market has moved since the last trade.