Close one eye, tilt your head to 45°, open eye uppermost, poke the tip of your tongue out of the corner of your mouth on the opposite side to the open eye. Hold this pose, facing the object to be measured, for 58.75 seconds, then slowly drawl "Hmmmm, I'd say xyz.abc* units."
*The more decimal places, up to three, used makes the measurement appear most accurate but four decimals make it look like a guess.

