I use the thick,flat black poster paper from Wal Mart. I put three layers of that shiny aluminum tape that you can get at hardware stores or auto parts stores in the center. The tape is 2 inches wide and I cut pieces 2 inches long.
I put this out at 50yds during the daylight hours when I first get to the range. By the time that I get setup,the cardboard is hot from the sun,and the tape that reflects the sun is cooler giving me enough heat differential to easily see the center tape target.
My scopes electronic clicks move about .3" with each push of the button and I move it onto center as I would any other scope. I have had my thermal on three different guns and it has never taken me more than 5 shots to zero. --- pruhdlr