Level II Components
The left portion of the screen represents the buyers, and the right side of the screen is the sellers. The yellow color code represents the inside bid and ask prices. The inside quotes are the highest the buyer is willing to bid, and the lowest the seller is willing to offer. Each additional color represents additional level of buyers and sellers at various prices.
Next to each price is a symbol, such as ISB or ARCA. These are Electronic Communication Networks, or ECNs for short. Instead of your order being routed through a broker, you send it through an ECN. Each ECN matches orders on the buying and selling side to facilitate a transaction. For example, the ARCA ECN is displaying a bid at $18.36, and an offer at $18.37. An ARCA order will not be filled unless a seller drops to the $18.36 or a buyer raises his or her price to $18.37. Please note that if you enter an order through a specific ECN, an order will only be filled if it matches that same ECN.
You may note that there is an additional number next to the price on the Level II screen. This number shows the amount of shares that are trying to be bought or sold. They are denominated in 100s, so a print of 32 equates to 3,200 shares. For example, through the ISB ECN 9,800 shares are willing to be bought at $18.35, while 11,200 shares are willing to be sold at $18.38.