A uniform electric field exists between parallel plates of equal but opposite charges. (Correct?) For electric field mapping with a general electric field mapping board, the electric field intensity, which can be calculated from the potential difference and distance between any two points, can vary or not be constant. This can arise from experimental errors. Aside from human error, why is there sometimes a lack of uniformity of the field between the plates? If the board has cracks, could this influence the electric field intensity in different areas? I don't really understand how an electric field mapping board functions.