I just picked up a used Bestwell Mini-Sight 10x grain focuser. Looking at the wire which is strung across the focusing reticle, I notice it doesn't lie flat across the opening. It has a little slack in it and bows down in the middle by maybe 5mm.

It seems to me that this wire should be taut and flat from one side of the reticle to the other. I have no reservations about "fixing" this myself, assuming it needs fixed in the first place. Since I've never seen a grain focuser up until yesterday, I don't know if this is abnormal. But, my understanding of how these work suggests that the bowed wire is wrong.

Can anyone else who has one of these confirm that the wire should be flat? Thanks!