Although fuzzy systems allow expression of expert knowledge in a more natural way, they still depend on the rules extracted from the experts, and thus might be smart or dumb. Some experts can provide very clever fuzzy rules – but some just guess and may even get them wrong. Therefore, all rules must be tested and tuned, which can be a prolonged and tedious process. For example, it took Hitachi engineers several years to test and tune only 54 fuzzy rules to guide the Sendal Subway System.