The blind spot mirrors on cars are becoming irrelevant tech. Many people now believe the side mirrors are rear view mirrors and mistakenly adjust them to look at the car directly behind, giving three views of the same vehicle. If you pull up behind such a car, you will see the driver’s face in the side mirrors.
Automobile side mirrors are not rear view mirrors. The rear view mirror is the one in the center of the windshield. The side mirrors are safety additions to cover “blind spots”. These are the areas behind and to each side where a car in the next lane is invisible when it pulls forward out of the rear view mirror’s field and isn’t yet far enough forward to see with peripheral vision or a glance to the side. Properly adjusted side mirrors allow you to see a car in the blind spots and avoid a potentially disastrous lane change or turn resulting in a collision that will be your fault.
The blind spot mirrors can be roughly adjusted while parked. Put the driver’s seat in its normal position and adjust the mirrors up or down until the horizon is in the middle of the mirror. Lean to the left until your head touches the window and adjust the left mirror until you can just see the side of your car at the right edge of the mirror. Lean the same distance to the right and adjust the right mirror until you can just see the side of your car at the left edge of the mirror. This procedure produces a good approximation and will cover most blind spots. The adjustment can be fine tuned in traffic as you observe whether you pick up passing cars in the next lane in the side mirrors before they leave the rear view field and whether you can see them with peripheral vision before they leave the side mirror fields. Even with properly adjusted mirrors there are still blind spots for cars two lanes away and also for cars on a highway when you are merging at an angle. But properly adjusted side mirrors will allow you to scan for converging traffic in these cases by moving your head and avoid an accident.
The really bad effect of this is that some current car engineers either do not know what the side mirrors are for, or kowtow to their marketing wonks who decided that customers do not know and shouldn’t be informed. As a result, the blind spot mirrors on some new cars cannot be adjusted to cover the blind spots and can only be used to give a duplicate rear view. Check this when you shop for a new car by trying the above procedure. If the mirrors can’t be correctly adjusted, register your dissatisfaction, go somewhere else, and save yourself from a potential accident.