In obstacle marking, the ratio used is which of the following?

• A. 5:1
• B. 3:1
• C. 10:1
• D. 2:1

Answer: (C)

Obstacle marking uses a standardized scale so pilots can quickly read hazards from the air. The 10:1 ratio means the visual cue is scaled so that markings grow proportionally with obstacle size, keeping them recognizable at the typical viewing distances and angles of air assault flight. This ensures larger obstacles have more conspicuous markings while smaller ones still present a clear cue, aiding pilots in judging distance and maintaining safe clearance. Ratios like 5:1, 3:1, or 2:1 would make the marks either too crowded or too faint to read quickly from the helicopter, reducing legibility and reaction time.