These were made by Kodak & probably other firms as well. They have a grid pattern & are used for aligning slide projectors. You mount the slide & project it on the screen & use the grid to get the projector correctly positioned. I do slide shows every week where I have to set up the projector just before I start, so having some of these target slides would be a big help. I'm sure it's an obscure product but APUG seems a likely place to start asking.