I have a question about testing your cya, do you fill the vial until the dot can't be seen at all, or until it just starts to fade out? Seems the more I look at it, sometimes I think I can see it and sometimes not...
See this link. Don't go crazy looking for it. If you are saying to yourself "I think there might be a dot, but I'm not sure", then it's probably not there. You can always add more to the tube to see if it changes, then pour some back in the bottle and do it again until you get a reasonable sense for it. It's more a matter of practice. What is important is to stand outside with your back to the sun holding the tube in front of you looking straight down into it. Hold the tube from the top so that you aren't blocking the strong indirect light into the sides of the tube.
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