To achieve a match, a normal trichromat sets the test scale to approximately what value on the Nagel Anomaloscope?

A normal trichromat setting the test scale on the Nagel Anomaloscope will typically place it around 17. The Nagel Anomaloscope is a diagnostic tool used to evaluate color vision. It works by presenting two fields of light, where the observer can adjust the intensity of one of the colors to match it with a fixed color. The normal setting for individuals with standard color vision is an indication of their ability to perceive and combine the primary colors—red and green—effectively.

In a normal trichromat, the number 17 on the scale corresponds to a specific wavelength that these individuals can perceive as a good match to the provided reference hue. This level reflects a functional and balanced perception of red and green that characterizes normal color vision. Other values on the scale may indicate different types of color vision deficiencies or variations in color perception among individuals. Therefore, the 17 setting is indicative of typical color vision function among trichromatic observers.