I'm getting set up to test a commercial mirror arriving tomorrow. It's 10 inch, f/4, 35mm thick, GSO manufactured. So far I've recommissioned my 20 year old Foucault tester from the dusty depths of my garage. I made an adapter to allow use of my DSLR to take test images. My question: how should I support the mirror in the test stand? would two support points at +/- 45 degrees offset be adequate, or do I need a sling of some sort? I am looking for reasonably accurate measurements; if the figure is smooth without astigmatism or turned edge or other gross defects, and wavefront error is less than about 1/4 wave, I will be happy. If it tests well it goes into my astrograph project. Here is my old tester, which last helped me make a very nice 12 inch f/4 mirror.