When should an operator use 10 NM range scale on the MMR?

• A. Life Raft Search - Use 10 NM range scale only briefly to investigate target
• B. During normal surveillance scans
• C. Only during overland navigation
• D. Never use 10 NM range scale

Answer: (A)

In radar work, how you choose the range scale is about balancing how much area you can see with how much detail you can discern. For a life raft search, you want broad coverage to quickly detect any potential targets across the search area. The 10 NM scale gives a wide field of view so you don’t miss distant targets. But this wide view comes at the cost of resolution, so when you spot something suspicious you should switch to a smaller, more detailed scale to inspect and confirm what it is. Using the 10 NM scale only briefly for this initial look keeps you from sacrificing detail during the ongoing search.

Other options don’t fit because regular surveillance typically benefits from higher resolution to track and identify multiple contacts, overland navigation involves a different environment with coast clutter, and there is a legitimate use for a wide view during search—so it isn’t something you never use.