Mirrors do not provide an accurately scaled image. Depending on your distance from the mirror (which will be different depending on the driver and exact setup), the scale of the objects depicted in the mirror based on their actual size and distance will vary. Even if your distance from the mirror is consistent, the relationship between image magnification, the distance to the object as it appears in the mirror, and the actual distance to the object requires high-school level physics that nobody has time to do in their head while driving. At best, mirrors are an imperfect solution to the problem of seeing obstacles while reversing.
Fortunately, we now have a much better solution: the reversing camera. A reverse camera kit allows you to see what’s behind you on a monitor at the front of your car. That monitor includes a clear, simple distance scale, eliminating the difficult guesswork involved in reversing. With a rear vision camera, looking behind you when you drive and reverse is no longer a haphazard process of estimation, but an accurate, reliable course of action. The best reversing cameras are connected by a cable to ensure no interference with the signal, so that if a cat suddenly runs behind your vehicle while you’re reversing, you’ll definitely see it.
The reversing camera kit is an absolute necessity if you’re driving a larger vehicle like a truck or RV, or if you’re towing a caravan. In such circumstances, the usefulness of mirrors becomes almost zero, so a reverse camera is the only safe way to get a sense of what’s behind you. You can attach a caravan reversing camera to your caravan, which means that you will know what’s behind your trailer and not just what’s behind your vehicle. Truck rear vision systems and motor home reverse cameras are also available, and make driving in these vehicles much safer.