Worked example — Class C ceiling math.

• Sectional fraction 41 / 16 on a Class C ring → ceiling 4 100 MSL, floor 1 600 MSL.
• Airport field elevation labeled 318’ MSL on the chart.
• Callout 718’ MSL = 318 (ground) + 400’ AGL limit = max legal drone altitude MSL at that spot.
• Takeaway: Part 107’s 400 AGL cap becomes a site-specific MSL number once you know the terrain elevation. Plan in AGL, report in MSL.