Reading Logan’s Class B ceilings.

• The fraction 70 / 30 means ceiling 7 000 MSL, floor 3 000 MSL (add two zeros to each number).
• The fraction 70 / SFC means ceiling 7 000 MSL, floor is the surface.
• All altitudes are in MSL unless in parentheses — if you see “(12)”, that’s 1 200 ft AGL.