Apple's market value touched $5.036 trillion (£3.79 trillion) on Tuesday afternoon before slipping back, making it the second company in history to reach the level. Market value is what investors think the shares are worth on a given afternoon, not money sitting in an account. The step from $2 trillion to $4 trillion took five years and two months. The step from $4 trillion to $5 trillion took nine. Apple got there by a different route, and the difference is the whole argument about what the company is now worth.