Establishing the sequence of intersecting ball-point pen strokes

At ball-point pen intersections a narrowing of the second line sometimes occurs. When the effect is sufficiently marked it can be used to determine the order of ink strokes with reasonably high probability of success. Attempts to treat the narrowing statistically using width measurements were not very successful. Another effect involving the casing of the pen dragging along a small amount of ink from a previous ball-point ink line can also provide a convincing determination of the line order.