llongwill® DISLab Equipotential Lines Tracer can accurately locate and measure the potential difference on conductive paper. With this app, it is possible to fit points with the same potential difference, draw equipotential lines, and complete experiments such as "drawing equipotential lines in an equal amount of heterogeneous point charge electric field", "drawing equipotential lines in a uniform electric field", and "drawing equipotential lines in a point charge electric field".