What can be checked to determine the quality of brake fluid?

To assess the quality of brake fluid, measuring the moisture content in the fluid is crucial. Brake fluid is hygroscopic, which means it absorbs moisture from the air over time. This moisture can lead to a decrease in the fluid's boiling point, which can result in brake fade or failure under high temperature conditions. High moisture content can also contribute to corrosion and reduced performance of brake components. Therefore, testing for moisture content allows for a direct evaluation of the brake fluid's effectiveness and safety.

The other options do not directly address the quality of brake fluid. For instance, checking the pressure of the brake system is important for ensuring that the braking force is adequate, but it does not provide information about the fluid's condition. The size of the brake components is relevant for fit and compatibility but does not relate to the fluid's performance. Finally, while temperature is important in the context of braking performance, it does not inform the quality of brake fluid itself. Thus, measuring moisture content is the most definitive method for evaluating brake fluid.