The number of deep book data windows that you can display at one time (including BookTrader, ISW and Market Depth) is equal to 1 for every 100 allowed lines of market data, with a minimum of three and a maximum of 30. Market data allowance is based on commissions, available equity and other criteria. So a client with the minimum allowance of 100 lines of market data will be able to open 3 deep book windows. A client with an allowance of 500 lines of market data will be able to open 5 unique deep book windows.