(ChinaFotoPress/Getty Images)

Apple, the world’s most valuable company, will join the Dow Jones Industrial Average on March 19, just in time for its stock to maybe explode up even more as it tries to convince us that we can’t live without an Apple Watch firmly ensconced on our wrists. It’s good news for the Dow, but a good reminder that the Dow is pretty meaningless.

Now, on its face, the news that Apple will be replacing AT&T in the Dow feels like the kind of thing that should tell us something about, well, something. The Dow, after all, is synonymous with stocks in a lot of people’s minds, so maybe this is a changing of the guard! iPhones are in, and the spotty network that they run on is out? Apparently. But what does that mean really?

Well, nothing. The Dow doesn’t have some supernatural significance, even if we treat it that way. It doesn’t have any significance, actually, except that it has retained this enormous symbolic value. It’s just a 30 company stock index that’s hand-picked to try to represent the whole market. And that’s the first problem: the sample is so small that the index itself can change a bit just because a few companies in it do. But the bigger problem is that the Dow averages these 30 stock prices in a way that makes approximately zero sense. Instead of weighting each stock price by the company’s size, each stock price is weighted by. the company’s stock price. In other words, they aren’t weighted at all. It’s just a normal average.

That’s beyond silly. Think about it. Apple just did a 7-for-1 stock split that lowered its share price to $128. So that means, when it comes to the Dow, Apple, with its $750 billion market capitalization, will count less than $190-a-share Goldman Sachs, with its $83 billion market capitalization. But it gets even sillier than that. The only reason the Dow is even adding Apple now, which seems way overdue for what’s supposed to be the blue-chip index, is that Visa is about to do its own 4-for-1 stock split that will lower its price, too. Why does that matter? Well, the Dow classifies Visa as an information-technology company, so its soon-to-be lower share price will lower the index’s technology weighting more than the Dow wants. The solution? To start averaging stock prices by a company’s actual size? No. It’s just adding Apple instead.

If you think that’s a good way to measure the stock market, then you’re probably a Dow Jones employee — because nobody else does.

Matt O’Brien is a reporter for Wonkblog covering economic affairs. He was previously a senior associate editor at The Atlantic.