The mechanism by which a market-maker creates each day's price bar in response to incoming buy and sell orders. When the market-maker is bearish, he gives buyers a good price (compressing the upper end of the range and producing a narrow-spread up-day); when bullish, he marks prices up against incoming buying (producing a wide-spread up-day). The resulting bar is therefore not a neutral record of trading, but a direct readout of the market-maker's sentiment on that session's activity.