Gaia DR2 parallax uncertainties versus parallax of all stars within a distance on the sky of 20 arcmin to the cluster center taken at the same position as in Fig. 1. The dashed and dotted vertical lines indicate the mean and limits of one standard deviation, respectively, of the parallaxes as determined by Caballero (2018) from cluster members. The red and gray solid lines indicate the parallax uncertainty limit at any given parallax below which the relative uncertainty is less than 20% and 5%, respectively. The positions of σ Ori C, D, and E in the diagram are indicated by the blue and red filled circles and the green filled diamond, respectively.