Comparison among different measures of the contribution of optical/IR (X-ray undetected) to the X-ray background. The gray area represents the best fit to our data. Green, blue, and red points represent the photometry of Hickox & Markevitch (2007), Luo et al. (2011), and Cowie et al. (2012). Black squares and arrows represent our photometric values and 2σ upper limits including systematic error of 2% on the background measure. Gray arrows show the upper limits accounting only for statistical errors.