It's not very accurate. People put fake bid/ask offers on the trading pad, then take them down the last minute to make you think the market has a large lot waiting to be bought up.
ECN buy and sell orders use to be online for free through Instinet and island. Warren Buffet owned one of them and use to give it for free. But now it cost money to look at it. They were giving real time "time and sales" online from the website.