X-ray colour-colour diagram (or HR diagram) of the elusive AGN. Gives a crude indication of the intrinsic X-ray spectral shape and level of absorption. The majority of the sources have a low HR (in yellow) consistent with being unabsorbed or having low absorption column density N_H ≲ 10²² cm^-2. The errors for both HR2 and HR3 range from about 0.01 to 0.2, with a mean values of respectively 0.08 and 0.09. The size of the typical (mean) errors is indicated by the black error-bars shown in the top left of the diagram.