We’ve come up with a reversible cross for our purificators. We don’t like it when the back side looks icky, and this is our solution.  You’ll want a magnifier, and make sure it's one of those that has the little inset bubble magnifier - and not just any bubble magnifier. We have two or three magnifiers that have the higher powered disk, but only one of them has a high enough power to comfortably count threads on fine linen. The one that works actually has a sharp edged lip around it on one side - think of those grade school kids you remember with the super thick glasses. This thing has an extra thickness, maybe 1/16" of extra magnification. Get that one.