My spectrodensitometer states its measuring geometry is 0/45, and its standard observers are 2 and 10. Are these angles related? Which should I use?

0/45 refers to the geometry of illuminating the sample (0 degrees from the normal, or perpendicular) and detecting the reflected light (45 degrees from the normal). That is unrelated to the two and ten degree observers. Those refer to the field size when the original experiments were done to determine the standard observers for colorimetry.

Think of them like have two different people look at the matches. Either observer would be appropriate for your application. It is best to be consistent, record which one you use, and use whatever is requested by your customers/suppliers or any standards you are following.

More on all these topics can be found in books on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed. More.

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