During the last 20 years, there has been discussion within the color research community regarding the accuracy of the <overline>x</overline>(λ), <overline>y</overline>(λ), <overline>z</overline>(λ) human observer functions and the variations among observers. Some studies have indicated disagreement between numeric vs. visual metameric matches when comparing white light sources or comparing hard copy vs. soft proofs. This paper describes a method for systematically improving the human observer functions in response to new data from proposed experiments that can be reproduced at multiple locations.