A marine engineer retires to the countryside
One day he's passing the blacksmiths shop and he sees the smith making horseshoes. "I can do that, " he told the smith. When he got home, the engineer made four horseshoes in his little workshop. The blacksmith is impressed. Each edge is milled , each hole is perfectly drilled, the finish is immaculate and all four shoes are identical. He tells the engineer to fit shoes to a horse while he goes home for lunch.
When the smith returns, the shoes are fitted, each one set dead centre, each nail trimmed and polished. "That's a great job you've done there, couldn't do better myself, only , why is the horse upside down?" "No idea,", said the engineer, "He's been like that since I took him out of the vice".