Thanks for your responses I guess what I am looking for is a system that will ideally tell me if there is overhang on a stock
e.g. sometimes huge quantities above the NMS can be bought/sold. This can sometimes give a good indication of a stock overhang, e.g. if you can buy 200,000 shares but only sell up to 2,000 online, there's a good reason to believe that the price won't be going up anytime soon (unless a big trade takes the available shares). If somebody sells 1,000 shares, the bid price may then move down.