Tesla stock is up again in midday trading Tuesday, by almost $7, or 1.5%. The S&P 500, by contrast, is down about 0.3%. It marks another all-time high for the electric vehicle pioneer.

Tesla (ticker: TSLA) shares are up a whopping 93% over the past three months and have soared almost 10% year to date, far better than the 0.4% gain of the Dow Jones Industrial Average. The recent run, however, is only part of the story. The gains have made Tesla the most valuable car company in America ever.

There was Henry Ford, then Alfred Sloan, and Lee Iacocca. Now Elon Musk gets his place on the American automotive Mount Rushmore.

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Tesla’s current market capitalization is approaching $83 billion and that exceeds the peak Ford Motor (F) market value of about $81 billion set in 1999, according to Dow Jones Market Data. Tesla’s market value is also larger than prebankruptcy General Motors (GM), current General Motors, and pre- Daimler (DAI.Germany) Chrysler or Fiat Chrysler Automobiles (FCAU). (Chrysler and Daimler merged in 1998.)

It is an amazing number, but there are a couple of caveats.

First, the statistic isn’t adjusted for inflation. General Motors was once the largest company in the world, back in the 1920s. The S&P 500, of course, was much lower then, trading for around 18 points.

(The market is more than 3,200 points now, up more than 177-fold over the past century or so.)

Today’s largest U.S. company is Apple (AAPL), worth more than $1.3 trillion, or about 4.3% of the nearly $30 trillion total value of stocks in the S&P 500. The percentage that GM represented of the total stock market in the late 1920s wasn’t available.

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The second caveat is about total market value, including debt. At different points in the past, Ford and General Motors have had large debt and unfunded pension liabilities, which can be debtlike—this also muddies comparisons of market value. Back in 1999, however, Ford’s pension was overfunded and automotive net debt—which is debt not tied to automotive finance—was low. The 1999 comparison, to Ford at least, is clean.

Regardless of the caveats, Elon Musk’s feat is impressive. He built a car company from scratch this century, and it is now worth more than any of the so-called Detroit-three auto makers at any point in history.

Write to Al Root at allen.root@dowjones.com