Multiply each value of 
in each series of observations
by the corresponding value of 
and plot the product
as a function of
for all the observations, positive and negative, on
the same graph. Can you predict what the result should be?
From the above graphs can you determine the value of the ratio
? How does the value compare to that obtained by
direct measurement
of the plates? Because of the "fringing fields" which extend
beyond the ends of the plates, their effective length is longer than
their actual length.