A Beaufortian scale for airplane turbulence

• 0, calm: No sensation of motion. Coffee in a cup is still.
• 1, light: Like driving on cobblestones. Coffee ripples.
• 2, moderate: Seats swerve and jerk. Coffee sloshes without spilling. Seatbelt light is turned on, though flight attendants continue their service.
• 3, severe: A rollercoaster ride. Coffee perilous to hold. Flight attendants take their jumpseats.
• 4, extreme: Frequent freefalls in every direction. Loose objects are projectiles. Airsickness bags are taken out and used.