Submarine

The navy’s most advanced submarine came to a halt and eventually limped into port.  The top repairers were contacted and none was able to fix the boat until one man was called.

He duly arrived, walked around the boat and eventually came to a halt in front of a pipe.  Taking out a small hammer, he hit it gently.  Amazingly, the submarine shuddered back in life.

The navy was very grateful and asked the man to send his invoice.  However, when it arrived, they were disconcerted to find it was for £100,000.  Summoning the man, they complained that this was far too much for simply hitting a pipe with a hammer.  Would he please resubmit his invoice in more detail?

So the man resubmitted:

“For hitting the submarine with a hammer, £100
For knowing where to hit the submarine, £99,900”