Which of the following is required safety equipment?

A crane level indicator is essential safety equipment because it helps to ensure that the crane remains stable and balanced while lifting and moving loads. This indicator monitors the levelness of the crane, which is crucial to prevent tipping over and maintain safe operation. If a crane is not properly leveled, it can lead to dangerous situations such as load swings or loss of control over the load, potentially resulting in serious accidents or injuries.

While the other equipment listed may have their benefits for specific conditions or operational efficiency, they do not replace the fundamental safety provided by maintaining the crane's level. The GPS tracking system can help with locating the crane or monitoring its usage but does not directly ensure safety during operation. The wind speed gauge is useful for assessing environmental conditions, but it does not contribute to the mechanical stability of the crane itself. An emergency service phone is important for communication in case of an emergency but does not impact the immediate safety measures during crane operation.