Which of the following items should always be checked before using a gauge?

The calibration status is crucial to check before using a gauge because it ensures that the instrument is providing accurate and reliable measurements. Calibration refers to the process of verifying that the gauge's readings correspond to the known standards or measurements. If a gauge is not properly calibrated, it can lead to incorrect data, potentially resulting in safety hazards, inaccurate assessments, and faulty decision-making. The integrity of the measurements obtained from nuclear gauges is paramount, especially in safety-sensitive environments.

While other aspects like the color of the gauge, the brand, and the user manual can provide information about the gauge, they do not have the same essential impact on the immediate safety and accuracy of its operation. Checking the calibration status is a critical step in ensuring that the gauge performs correctly and that the readings it provides are trustworthy.