Movement of charge can be characterized in terms of a number of dipoles. Dipoles have a (-) tail, (+) head. The vector equals the sum of the dipoles.

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If exploratory electrode is placed right of center, (+) charge is encountered & a positive deflection results.

If exploratory electrode is placed left of center, it encounters surface negativity & the result is negative deflection.

If electrode is placed above or below the horizontal line at an oblique angle the amplitude of deflection decreases.

If electrode is at midline, ie. perpendicular to the dipole, no electrical signal is seen due to charges cancelling out.

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