I acquired an X-Rite 811 densitometer and their website wants $110 for the transmission and reflection calibration targets. The reflection target looks nothing more than white/black/grey dots on a small card. The transmission is a 4 step wedge (I assume transparency/slide). I want to use Stouffer's 21 step targets (Reflection and Transmission), but which 3 or 4 would I use for calibration. I like the idea of the Stouffer products since they have other uses and they are $6.55 each.