On Wednesday, October 12, 2016 at 2:25:53 PM UTC-5, wrote:
When I bought my Ventus, it had Two rearview mirrors mounted to the glare shield each was about 3 inches in diameter and convex type. I found them totally useless. There is no way you are going to see someone in them yet alone avoid them unless your constantly staring at it. Add to the fact that they considerably blocked my forward view they went first, then I took off the Hamilton vertical card compass next. The next 2500 hours in the plane were much more enjoyable.

If he's flying a motorized glider, the mirror may be used to confirm pylon position. I found a similar, small, convex mirror at an auto supply store.