German figure of speech when making a rough estimate. Usually accompanied by a gesture of squinting over the top of your thumb while wiggling it around :) Literally it means "pi times thumb", I don't know if there is an equivalent in English.

Apparently the origin lies in a way to estimate distances by making use of the parallax effect ("Daumensprung"). You extend your arm in front of you, close one of your eyes and raise your thumb so that it's in front of the object in question. Now when you close the eye and look with the other one the object seems to make a jump. Estimate how far and take it times ten, that's roughly how far the object is from you (basic geometry, you arm is about ten times as long as your eyes are apart).

(a nodeshell rescue)