Determining locations of electro-optical pens. A disclosed example includes, a distance determiner to determine a distance from a pen to a scribing plane at a plurality of points to produce a plurality of distance measurements, a tilt orientation determiner to determine a tilt orientation of the scribing plane relative to the pen based on the plurality of distance measurements, a plane of view corrector to, based on the tilt orientation of the scribing plane, correct a plane of view associated with at least one of the first perspective and the second perspective, and a coordinate determiner to determine coordinates of the pen based on the corrected plane of view. A location determiner determines the location of the pen on a display based on the coordinates.