This off angle speed measurement error is referred to as the COSINE error, named after the mathematical function that allows you to calculate the exact speed versus angle. The measured speed will always read lower than the actual speed as you move off the centerline of the path of the moving object. For small angles, this error will be very small. This is why you see police officers pointing their radar along the direction of the road; not down a side street pointing sideways to the road.Each degree from center will cause your speed to read the noted % lower.The table below shows you how speeds slow down the farther you are from center.