I do hate sums.  There is no greater mistake than to call arithmetic an
exact science.  There are permutations and aberrations discernible to
minds entirely noble like mine; subtle variations which ordinary
accountants fail to discover; hidden laws of number which it requires a
mind like mine to perceive.  For instance, if you add a sum from the
bottom up, and then again from the top down, the result is always
different.
		-- Mrs. La Touche (19th cent.)