When the Show Intraday P&L option is selected via the right-click Menu, you will see the Intraday Profit & Loss displayed on the left-hand side of the Price Alerts Window.
The Intraday P&L is based on your Price Alerts. It is calculated by comparing the current price of the stock to the Price Alert Level. The total sum for today is displayed as the Intraday P&L.
The Intraday P&L shows if your Price Alert and the chosen direction, long or short, have worked in your favor or not.