I am getting my CYA up after a new liner installation and have a question about reading the number. I noticed when you hold the tube at the top with your fingers, the reading is higher. The dot disappears sooner. But if you cup your whole hand around the tube like my husband does, you see the dot longer and the number is lower. Cupping the tube blocks most of the light out of the tube. So I'm thinking it should be held at the top with your fingers, not blocking the light from going through the tube. It seems to make a difference of about 10 points. That's quite a bit. And we are standing with our back toward the sun like it tells you to do.
Thanks for your input.