Long-range radar sites turn at a rate of 5 rotations per minute. In other words, it takes 12 seconds to make one complete sweep. So, in our example here, to rotate 225 degrees will have taken 7.5 seconds. If the airplane is traveling at 2 miles per minute (120 miles per hour), in 7.5 seconds it will have traveled 1/4 of a mile from the time radar A saw it, till radar B saw it. That is what makes it look like two aircraft flying in formation on the display if double-preferred adaptation is utilized.
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