TradeStation Help
This option allows you to hide the true number of shares that you wish to buy or sell. To do this, you select the total quantity for the order and the quantity that you want displayed. This helps minimize the impact on a market when trading a large number of shares.
For example, if you want to sell 10,000 shares of stock ABCD but don't want to shock the market by displaying the entire number in the window at once, you can choose to display your shares in groups of 1,000. When a group of 1,000 shares is sold, another group of 1,000 shares will appear in the Market Depth window. Your order will be dispensed in groups of 1,000 shares until it is completely sold.
This Advanced setting is available only with specific order routes.