Graph X is the first Heart Rate Monitor with a color graphical display. The three color display works on a similar principle to a tachometer in a car, and shows how hard the heart is working during exercise compared to the active target zone. Cardiozone lets you set a target zone while actually exercising. Once a desired workout level has been reached, a key press activates and sets cardiozone, which works like a cruise control on a car, keeping you within the selected workout level. Xtreme has a powerful 100 hour chronograph with up to 100 lap and split times on screen and has 99 memories for lap time with average heart rate and split time. Xtreme is an excellent partner for interval training with automatic heart rate recovery on either a time or heart rate basis. It also features a countdown timer up to 99 hours.