What must be done to the Federal gauge before it can be used to inspect the countersink?

To effectively use a Federal gauge for inspecting countersinks, it is essential to ensure that the gauge is zeroed. This means adjusting the gauge to ensure that it provides accurate readings starting from a known reference point, essentially ensuring that the measurement begins at zero when the gauge is in contact with a flat surface. This step is critical, as any errors in zeroing can lead to inaccurate assessments of countersink depth or diameter, which could potentially result in improper fit or structural integrity issues in the assembly process.

Calibration is an important part of maintaining measurement instruments, but it typically refers to verifying the overall accuracy of the tool against a standard, rather than adjusting it for a specific measurement task. Cleaning the gauge is also important to ensure that dirt or oils do not interfere with the measurement, but it does not address the need for establishing an accurate baseline measurement. Repairing the gauge is necessary only if it is damaged or malfunctioning, which is not a routine requirement prior to every use.

Zeroing the gauge is, therefore, a fundamental step in the inspection process that ensures the accuracy of the measurements taken, especially in the context of critical aerospace applications where precision is paramount.