Explanation: Compulsory GMDSS (Global Maritime Distress and Safety System) equipment, such as VHF-DSC (Digital Selective Calling) radiotelephones, is critical for maritime safety and distress alerting. To ensure these vital systems are fully operational and ready for immediate use in an emergency, international SOLAS (Safety of Life at Sea) regulations, which form the basis of GMDSS, stipulate a minimum daily test for certain equipment by the ship's crew while at sea. This daily operational check verifies essential functions, such as power supply, antenna connection, and the ability to initiate a routine DSC call. It ensures the equipment remains in a state of readiness between more extensive weekly or monthly checks and annual surveys. Weekly, monthly, or annual checks by external representatives are insufficient to guarantee the constant operational availability required for distress situations, making daily verification the mandatory minimum interval.