The spot or convex mirror is probably the most under utilized piece of safety equipment that people have on their RVs. Most people do not understand the most effective way to use them.
I find after talking to people that spot mirror is not used to their full potential. Most people only use them when they are making a tight maneuver, and not using them during general driving. Think of you spot, or convex, mirror as an early warning device. They should be checked every time you check your flat mirror, which should be about every 8 seconds. 30% of the hazards that you encounter when driving come from the rear. Things will show up in the spot mirror sometimes several seconds before you detect them in the flat mirrors. This will give you additional time to take whatever action, if necessary, to avoid an incident. During driver training, in controlled conditions, we will cover the flat mirrors and make the student drive using the spot mirrors only.
Another thing that I have noticed is that when people install those stick on spot mirrors they generally put them in the wrong place. Most people will place them at the outside lower corner of their mirror. What they are doing is robbing them the use of the most important part of the flat mirror. When you look at the inside lower corner of a side mirror you will usually see the side of your vehicle. If you install the spot in the inside lower corner you will not change the view of the spot enough to notice and you will still get the maximum view from the flat mirror.
Learn more about how to set and use mirrors and many other heplful hints in the book “Drive Your Motorhome Like a Pro” available at RVDriveSmart.com.