However. as shown in MII-STD-883, Method 3015 (ref 7), we find that the decay rate is exponential(see fig 6a)in face, the complete discharge of a 5-kV charge may never reach zero if the earth itself is " an arbitrary zero of potention" thus depending on the quality of a ground at any given point, some residual voltage may remain on a grounded person or work surface (fig 6b)