The X-Rite plate reader's have the ability to determine the screen angle and LPI of conventional (not FM) screens. It does so by locating the centers of the dots and then determining the distance between these center points as well as the angle between them. The instrument can only provide this data when it can accurately determine where these center points are. Because of this, the instrument does not always display this data when measuring dot area. It is not possible to give a range where this occurs as it depends on the dot structure. Preliminary results indicate that with most screening conventions you will get readings in the 20% to 40% range. Again this will vary. Some customers have reported readings in two ranges with Euclidian dot structures (i.e. 20% to 30% and again 60% - 80%). This is logical with this dot structure because in the higher region it can detect non-image dots on the image area background. Customers using an elliptical dot structure may find that the instrument can calculate these values within a smaller range due to the shape of the dot.
Obviously the screen angle that is displayed is dependent upon the placement of the instrument.