The Market Depth / Level II Module provides bid/ask data, allowing you to easily monitor the depth of a given Symbol.
Level II can be a stand-alone Module...

Or it can be combined with Time & Sales in a combined Module...

In the first two columns of the Depth/Level 2 data area, the eight colors are simply used to separate the data (based on price). In the third - Time & Sales – column, green signifies “up”, red signifies “down” and white signifies “no change” in price.
The up and down arrows that appear in the Price columns of the Bid & Ask offer areas of our Depth/Level 2 data area are drawn based on the Bid/Ask delta value meaning that the specific Market Maker dropped or lowered their bid/ask value for that specific offer.
The "Exchange" identifier symbols are the Market Maker ID's for the various exchanges placing the bid & ask offers. Most can be clicked to view the details of the Market Maker.