While the error won't help, if the user finds and maintains track of the bright spot, they should do okay - if they "hunt" for it when they lose it in the center, they should find it again, since any motion of the mirror pulls the "bright spot" back out of the hole to the edge of the retroreflective annulus.

You can see what Doug is talking about in this YouTube video in the segment from 00:40-00:51, where the "bright spot" (red, in this case) momentarily disappears a few times when the mirror bobbles enough to head the "bright spot" towards center, at which point it disappears, but since any tilt after that brings it towards the edge of the hole again, it gets picked up.

(If you want to see this full screen or the like, here's the link to the original YouTube video: DIY Signal Mirror



It is some help to let students know that they should pass the very center of the bright spot across the target, since the "bright spot" is about triple the width of the main beam.

There was some confusion in some of these posts as to whether the diagram was depicting the "bright spot" or the sun itself - not too surprisingly, because the "bright spot" is an image of the sun. One nice thing about the red aimers - it is easy to tell a red "bright spot" from the sun.

Here's a photo I took of the (white) "Bright Spot" that makes it clear the "bright spot" is not the sun, since my hand is in the way:



Here's a photo showing the "bright spot' at the edge of the mesh, as Doug was talking about (and again - that isn't the sun, it is the "bright spot" - the sun is to the right of the photo scene):