Magnitude and position errors and their correlations in Houtman. The top frame shows the distributions of magnitudes according to Houtman for securely identified stars (identification flags 1, 2; red) and for not securely identified stars (flags 3–5; blue), and of the magnitudes in the Hipparcos Catalogue for all securely identified stars (black) in the large frame, and for each magnitude according to Houtman separately in the small frames. The middle frames show the errors Δα in right ascension and Δδ in declination as a function of right ascension and of one another, and histograms of the position errors for the securely identified stars separately for Δα (red) and Δδ (black). The numbers indicate stars within the frame (middle) and outside the frame to the left or right. The lower frame shows the distributions of position error Δ, for all securely identified sources in the large frame, and as a function of magnitude in Houtman in the small frames. The numbers indicate stars within/outside each frame.