Estimate Speed or Distance of Objects with the Hand
Calculator for speed and distance of moving objects, like planes or cars. Stretch one arm and take the time it needs, until the object has passed behind the hand, which means that it has passed a certain angle. The stretched pinky (fingertip for each finger) covers about 1 degree, the thumb 2 degrees, the three middle fingers together about 5 degrees, a fist about 10 degrees and a fist with stretched pinky and thumb about 20 degrees. If distance or speed are known, the other value can be calculated. This requires the object moving perpendicular to the line of sight. For a passenger plane, which isn't starting or landing, a speed of about 900 km/h can be assumed.
Formula: r = v * t / α
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