English: This image shows a simulated signal as displayed on the range scope of a restored AI Mk. IV radar, the first operational air-to-air radar system. Range increases towards the top, where the ground return would form a large triangular shape when used in operation. The large return at the bottom of the display is caused by the transmitter system, a small amount of this signal bleeds over to the receiver and overpowers any returns from aircraft. This limits the radar's minimum range to about 400 meters. Further up the display are two additional "blips", representing potential targets. By comparing the width of the blip on either side of the centreline, the operator can determine which direction the aircraft should turn to intercept the target. For instance, the larger upper blip is clearly longer on the left, so the aircraft should turn to the left to intercept. When the blip has the same size on both sides of the display, the aircraft is headed toward the target, within about 5 degrees. The system used two displays like this one, one displaying the "horizontal situation", as in this display, and a second one, normally located to the left, displaying the "vertical situation". The operator had to interpret both displays and give instructions to the pilot.