Edge-on view of the fundamental plane with mass as dependent variable. Here we plot all data realized N times to show the correlated uncertainties. Colors are as in Figure 2, and symbols indicate whether the source is an AGN (red circles), a Seyfert AGN (red circle with cross), an XRB in a low/hard state (blue squares), or an XRB in an intermediate or high/soft state (blue triangles). Each source is sampled from its measurement uncertainties as is done in the fitting procedure and is plotted with a partially transparent symbol plus a dark outline symbol on top at the nominal values. We plot the best-fit relation as a dark gray line with a light gray shaded region to indicate the 1σ region of the Gaussian intrinsic scatter, which has magnitude of 1 dex. This figure summarizes the results of the fits as well as indicates the fidelity with which one can use the fundamental plane to estimate black hole mass.