A built-in light sensor dims the display automatically at night, and increases brightness in direct sunlight. A ten segment bargraph display shows amount of retard, and thus gives an indication of the engine's tendency to knock at any particular time. The monitor is conected to the J&S SafeGuard with a 3.5 mm stereo cable supplied in the kit. The new SafeGuard units have an onboard LED that glows in proportion to the amount of knock retard. This will assist you in setup of the SafeGuard, but the bargraph gives much more information. The display shows how much timing is being taken out by the SafeGuard. When the SafeGuard is set for 20 degree control range, each LED is worth 2 degrees. If the SafeGuard is set for "retard all", and it is taking out say 12 degrees of timing, then you would see the 6th LED on. If the SafeGuard is set for "retard separate", then the display becomes more complex. Since the SafeGuard can retard each cylinder by a separate amount, you will see one LED on for each cylinder that is being retarded, and the position of that LED indicates how far. For example, let's say that one cylinder is retarded 4 degrees, another 6 degrees, and another 8 degrees, then you would see the 2nd, 3rd, and 4th LEDs on.