On the morning of every trading day on the Chicago Board Options Exchange, "Designated Primary Market Makers" set the skew for the options for which they are responsible. As the underlying stock price or index value changes, Autoquote uses this skew and the Cox-Ross-Rubinstein model to generate prices. If trading conditions shift markedly, the primary market maker can reset the skew during the day, but this by no means always happens.

Donald MacKenzie, An Engine, Not a Camera, loc. 907