Quote:

---

Secondly, the human eye is incredibly good at seeing flaws that are difficult to measure or photograph. Take a seemingly perfect polished metal cylinder and sight along it at a low angle and look at the reflection of a light on its surface as it is rotated. Any flaws will be obvious, but I'd have an extremely difficult time photographing it or measuring it with a runout gauge. As Wright mentioned a simlar technique is used when you inspect shotgun bores. For a flat metal surface, any distortions in a reflection of a grid pattern indicate unevenness that I can see but can't measure. I think OSR is very much a similar situation. My 2 cents.

---