Thumb bearing
Under Daumenpeilung is understood in the nautical an angle measurement by means of the thumb outstretched on also outstretched arm.
Since body dimensions such as the width of the thumb and arm length are roughly proportional, the angle measured in this way is relatively independent of the absolute width of the thumb and the height of the person taking the measurement - although it is still comparatively imprecise. A thumb's width corresponds to an angle of 2 ° - for example, if the upper edge of the sun is a thumb's width above the horizon, the sun will have set in eight minutes.
You can measure with the hand in a similar way: four fingers of the hand (at its root) correspond to an angle of 8 °, the entire hand with the thumb 10 °, the spread thumb and little finger spread an angle of 20 °.
In a figurative sense, the term “thumb bearing” or the expression “bearing over the thumb” is used for any type of rough and inaccurate measurement or estimate .