What is the scale range of vacuum indicators measured in inches of HgV?

The scale range of vacuum indicators is primarily measured in inches of mercury vacuum (inHgV), which is a standard used to express the level of vacuum relative to the atmospheric pressure. A full vacuum corresponds to 30 inches of mercury in a standard atmosphere, meaning any reading the vacuum indicator can provide will typically peak at 30 inches of HgV. This is a common measurement in various applications, including medical gas installations and other systems requiring precise vacuum levels.

When considering the other options, they represent values that are either insufficient to provide a complete vacuum measurement or exceed the standard measurement parameters for typical vacuum indicators. A reading significantly above 30 inches would not be applicable since, in practical terms, it would imply a super vacuum, which does not exist under normal circumstances. Hence, 30 inches serves as the upper limit, confirming its significance for vacuum indicators.