Returns a numerical value, indicating the current unrealized profit or loss for the open position.
- This function can only be used in signals.
- Will return a value of 0 if the current position is flat,
- Will return a value of 10 if the value of the open position has increased by $10 since it was entered,
- Will return a value of -5 if the value of the open position has decreased by $5 since it was entered.