This registry entry sets the 2D option in the Construct Ellipse dialog box if it is set to 0 (False). It sets the 3D option if it is set to 1 (True).
Entry Name: Constructed Ellipse - 2D3D
Entry Type: Whole number - either the default value 0 (False) to select the 2D option in the Construct Ellipse dialog box, or 1 (True) to select the 3D option.