A turn of the screw

A turn of the screw

There was an industrialist whose production line inexplicably breaks down, costing him millions per day. He finally tracks down an expert who takes out a screwdriver, turns one screw, and then - as the factory cranks back to life - presents a bill for £10,000.

Affronted, the factory owner demands an itemised version. The expert is happy to oblige: "For turning a screw: £1. For knowing which screw to turn: £9,999."