Flag pole.

[lenny]

Paddy and Mick are arguing about the height of a flag pole they are passing on the way to work, Paddy says it must be at 20 meters high Mick says its less than that its only about 15 meters high. A man hears the argument and says i can easily sort your problem out. He unscrews a nut at the bottom of the flag pole allowing the pole to lie flat on the ground, then takes a tape measure from his pocket measures it and tells them its eighteen meters, and then carries on his way.Paddy turns to Mick and says that man is thick we wanted to know the height not the length.