Explanation: A sweep secondhand is crucial for a ship's radiotelegraph station for precise timing in two critical operational scenarios. First, it enables the accurate timing of the specific durations of tones and silent intervals within the auto-alarm signal. This signal uses precise timing (e.g., 250ms tones, 500ms silence) to be effective, and an operator needs a sweep secondhand to manually monitor or verify these characteristics, ensuring the alarm system operates correctly. Second, it is essential for accurately timing the mandatory silent periods (e.g., 3 minutes every hour on 500 kHz). During these periods, all stations must maintain strict radio silence and listen for distress calls. Precise timing ensures compliance with these regulations, maximizing the chance of detecting faint distress signals from other vessels. Both functions demand sub-minute accuracy that a sweep secondhand reliably provides for maritime safety.