I'm becoming increasingly curious about the 'tunnel binaries' offered by IG Index. The section explaining them on the IG Index web site is very vague, simply saying that if the price fails to breach one of two pre-determined levels (one above and one below the previous day's close) the bet will settle at 100, but if the price does breach one of these levels the bet will settle at 0. What I don't understand is exactly what happens when you enter a tunnel bet. What does your P/L shows as when you've entered? What happens to your P/L if the price moves closer to one of the price limits? Can anyone explain exactly what happens from the beginning to the end of a tunnel bet and how the P/L changes with time and price movements?