What are the two ISO standards for balancing techniques?

The correct choice identifies ISO 20806 and ISO 21940 as the two relevant ISO standards for balancing techniques. ISO 20806 specifically provides guidelines for balancing machines, ensuring that they operate optimally and maintain accuracy in measuring the unbalance of rotating components. This is crucial for effective balancing, as it directly affects the performance, efficiency, and longevity of machinery.

ISO 21940 complements this by offering detailed requirements and procedures for the balancing of rotating machinery, including the various methods and tolerances necessary to achieve effective balance. Applying these standards ensures that equipment operates smoothly and reduces wear and tear, which is essential for reliability engineering.

The other options do not pertain to balancing techniques. For example, ISO 9001 and ISO 9002 focus on quality management systems, while ISO 14001 and ISO 45001 relate to environmental management and occupational health and safety, respectively. Lastly, ISO 50001 and ISO 22000 deal with energy management systems and food safety management systems, which are distinct from balancing practices in engineering contexts.