The trick: Standard atmosphere starts at +15°C at sea level and falls 2°C for every 1,000 ft you climb. The difference between the actual outside air temperature and that standard is your ISA deviation.

• ISA temp = 15 − (2 × altitude in thousands of feet)
• Deviation = OAT − ISA temp (positive = warmer than standard = thinner air = worse performance)

Worked example: At 5,000 ft, ISA = 15 − (2 × 5) = +5°C. If the OAT gauge shows +12°C, deviation = 12 − 5 = ISA +7 — warm day, expect a longer take-off run.

How to play. Each round is 12 questions. Start in CADET mode — just the ISA temperature for a given altitude. Once that's automatic, move to PILOT for the full deviation calculation at light-aircraft altitudes. When the trick is second nature, try TOWER — jet altitudes (FL200+) where ISA is well below zero, against the clock with a bonus for the high stuff. Every answer is a positive whole number — there's no minus key. Beat the top 10 and you'll be invited to add your callsign to the leaderboard.