The tradesman can read our vials from any position in a 300 degree arc, without parallax problems. He does not have to position himself at 90 degrees to the vial and bubble in order to get an accurate reading. The barrel is CNC machined using a diamond router. It is then polished. They are always fixed at the same position.
Some Asian manufacturers paint the rings on after the fluid is inserted.
We do not want any minuscule part of the bubble to hide behind one of the reading rings. This gives us a very accurate vial. The eye readily detects differences of one ten thousandth of an inch, so the reading of the difference in proximity to a reading ring from one end of the bubble to another is the least of anyone s problem. Because we cut the fluid barrel into a solid acrylic block there is no dead air space in the measuring area. Therefore, our vials can never fog.