Final answer:
The ARPA must calculate the CPA and TCPA with at least 95% accuracy, typically in real-time for navigational safety.
Step-by-step explanation:
The student's question pertains to the performance requirements of the Automatic Radar Plotting Aid (ARPA), which is a system used on ships to prevent collisions at sea. ARPA must calculate the relative motion between the user's ship and other contacts with a minimum accuracy of 95% for the Closest Point of Approach (CPA) and the Time to Closest Point of Approach (TCPA). The question does not contain enough context or provide a standard time frame to give a definitive answer. However, the typical time frame for TCPA and CPA calculations in radar systems is often immediate or in real-time as it is crucial for navigational safety. The accuracy of such calculations is critical to avoid collisions and is part of the ARPA's core functionality.