Thanks Jorge! I completely forgot about Stouffer. I have a 4x5 step tablet around here somewhere, but its uncalibrated. Thanks for the offer Clay, but I think I'll go ahead and buy the stouffer ones(transmission & reflection), since the prices are so attractive. Somehow I won this unit for a whopping $20 and it arrived today. To my suprise, it measures UV density too! I tested a few negatives, and everything seems to be in working order, but I wanted to check something of a known density so that I knew for sure. The calibration sticker says that it was last calibrated about this time last year.