What tool is commonly used to calibrate a micrometer or check its accuracy?

A gauge block is the tool commonly used to calibrate a micrometer and check its accuracy because it provides a precise length standard. Gauge blocks are made from high-quality materials and come in a variety of sizes, allowing for exact measurements to be supplied. When a micrometer is measured against a gauge block of known thickness, it ensures that the micrometer's readings are accurate. This is essential for maintaining high precision in measurements, especially in mechanical and engineering applications.

Using a gauge block for calibration helps identify any discrepancies in the micrometer's readings, which can occur due to wear, damage, or manufacturing tolerances. It allows technicians and engineers to correct any inaccuracies and ensure that the micrometer is functioning properly.

Other tools mentioned, such as a Vernier scale or caliper, also serve important roles in measuring but do not offer the same precise standardization for calibrating a micrometer. A protractor, on the other hand, is specifically designed for measuring angles, and thus is not relevant for micrometer calibration.