The Dow closed above 40,000 for the first time. The number is big but means little for your 401(k) WSB-TV Channel 2 [Video]

NEW YORK — (AP) — The Dow Jones Industrial Average just closed above 40,000 for the first time, the latest pop in what’s been a surprisingly good year for Wall Street.

But just like New Year’s represents an arbitrary point in time in the Earth’s revolution around the sun, such milestones for the Dow don’t mean much inherently.

For one, with just 30 companies, the Dow represents a tiny slice of Corporate America. For another, almost no one’s 401(k) account sees its performance depend on the Dow, which has become more of a relic used for historical comparisons.

What’s more important is that the Dow at 40,000 is one example of how the broader U.S. stock market is setting records.

Here’s a look at what the Dow is, how it got here and how its use among investors is on the wane:

WHAT IS THE DOW?

It’s a measure of 30 established, well-known companies. These stocks are sometimes known as …