What is considered an effective stop for a gauge?

An effective stop for a gauge is considered to be the indicating point at zero. This point is critical because zero represents the baseline measurement for pressure or level in many applications. When a gauge is calibrated, it is essential that it returns to zero when there is no pressure or when a pressure equal to ambient conditions is applied. This ensures accurate readings and the reliability of the gauge over its operational range. The zero point allows operators to determine the actual pressure when reading the gauge, making it an essential reference for safety and operation in high-pressure systems.

The other options do not fulfill the role of a standard reference point in the same way. The highest point on the gauge is usually at the maximum pressure capacity, while the lowest point does not provide a clear reference for zero pressure. A point halfway up the range may not correspond to any specific operational condition and could lead to misinterpretations of the gauge's readings. Thus, the zero point is critical for effective gauge functioning and is why it is recognized as the effective stop.