Originally Posted by Michael TLV
All the blue filters are not accurate. They were designed for CRT phosphors.
The purpose of the filter is to get you into the ballpark of where correct should be. You use your eyes as the final determiner after that.
The Spears and Munsil disc came with a one eye filter that had three options - 1x, 2x, and 3x for their blue filter. I've never heard doubling or tripling the blue filters mentioned on these forums. What effect does that have as to accuracy?