So here we are at the middle of 2013 already. The Dow Jones Industrial Average (DJINDICES:^DJI) is up 1,950 points -- or 15% -- year to date. Which companies led the index to these huge gains? The answer is not as simple as you might think.

Dow Gains in 2013.

The biggest winners in terms of straight-up percentage moves are pretty obvious. Hewlett-Packard (NYSE:HPQ) has soared 77% year-to-date on hopes that its turnaround efforts might be gaining traction. Yours truly happens to disagree. I still believe that HP needs to refine its business strategy much further and perhaps split into two separate entities. But you can't argue with the voice of the markets. So far this year, my bearish CAPScall on the stock has proven horrendously wrong.

Likewise, Boeing (NYSE:BA) bounced back strongly from niggling concerns about its big 787 Dreamliner bet. The high-end jumbo jet has overcome safety challenges and battery mishaps, and now looks like a solid best-seller worthy of Boeing's marketing focus. Share prices responded by doing their best impression of a Dreamliner on the runway, soaring 39% higher.

But these are not necessarily the largest drivers of the Dow's overall gains.

Switch your chart to the "Dow Points Change" view. The formerly smooth progression from large gains to small ones suddenly becomes a jagged roller coaster.

Boeing still hangs on to the upper echelons, and actually delivers the largest point gains at midyear by dint of its triple-digit share price. The stock delivered 225 fresh Dow points so far in 2013.

But HP is nowhere to be seen. Its modest 84 added Dow points ranks in the middle of the pack -- the 12th largest gain among 30 components. That's a side effect of HP's shares trading in the low double digits. HP's counterintuitive lack of impact on total Dow scores is perhaps the strangest side effect of the Dow's price-weighted nature in 2013.

Other anomalies include Caterpillar (NYSE:CAT) falling 7% on slow investments in global infrastructure construction. Thanks to the CAT's large share price, this move dragged the Dow down by 47 points. For a sense of scale, that's more than the 40 points that Cisco Systems (NASDAQ:CSCO) brought to the table -- with a huge 27% move to the upside. Cisco's long-term vision of dominance across the data center is finally coming together and the market is responding strongly. But like I said, this 27% jump makes less of a difference to the Dow than Caterpillar's much smaller 7% move.

Play around with the chart to get a sense of which Dow stocks matter the most to the index's point collection. Some of the answers might surprise you.

Fool contributor Anders Bylund owns shares of Intel, but he holds no other position in any company mentioned. Click here to see his holdings and a short bio. Check out Anders' bio and holdings or follow him on Twitter and Google+.

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