<p>In order to enhance the operationality of input work and computation, in a preferred mode, an arithmetic section retains a conversion formula for converting the total absorbance as a function resulting from absorbance measurement value weighting and linear combination to a water contamination level to thereby compute the water contamination level from an absorbance measurement value. The conversion formula is fed via a detachable external memory medium from an operational unit. The operational unit computes a conversion formula at its conversion formula computing section on the basis of water contamination level analytical value inputted from an input section and absorbance measurement values at multiple wavelengths on multiple samples from an analytical instrument having been given via the detachable external memory medium, and feeds the computed conversion formula via the external memory medium to the analytical instrument.</p>
