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A: Warren Buffett's Berkshire Hathaway made stock market history in October when it became the stock with the highest closing price ever: $100,000.

When a stock hits $100,000 a share, it's a jaw-dropping event. You can read more about the milestone here.

But it's important to remember that a better measure of the value of a company is market value, which is the number of shares times the stock price. And when you do that, Berkshire Hathaway doesn't seem so exceptional. With a market value of almost $162 billion as of late October, it ranked 13th among the Standard & Poor's 500 stocks in market value. No. 1 was ExxonMobil, worth almost $426 billion.

Should you buy the stock? First, keep in mind that class A and class B shares are similar and you do the same research if considering either one. To learn more about Berkshire's share classes, read this.

To find out if you should buy the stock, we'll put it through our usual four-step test:

Step 1:  Evaluate risk and reward. We start by downloading the stock's trading history back to 1990, which is the furthest my database goes. This analysis shows us something everyone probably already knows: Berkshire Hathaway has been a big winner. The average annual return since 1990 has been 18.8%, which is almost twice the long-term average annual return of the Standard & Poor's 500 stock index. Big returns, such as a 57.4% and 52.2% gains in 1994 and 1998, helped power the stock. The biggest loss during that period was a 19.9% drop in 1999, as investors went tech crazy.

But return is only half the answer. You have to consider the risk you took to get that return. And in Berkshire's case, the risk (or standard deviation) is 20.9 percentage points. In other words, most of the time that stock is either up 41.4% or down 0.4% or somewhere in between. You have gotten 0.9 percentage points of return for every percentage point of risk.

Compare that with the Standard & Poor's 500, which between 1990 and 2005, posted a 10.5% average annual return, says S&P. And the risk: 17.9 percentage points. That means you got 0.59 percentage points of return for every percentage point of risk. So in this 16-year analysis, Berkshire is one of the few companies that beats the market in the risk-and-reward test.

Step 2:  Consider the company's expected future cash flow. One way to evaluate a stock is to value the cash flow it's expected to generate as if you got it all today. A system from NewConstructs.com makes this easy. Entering Berkshire into the system returns a "neutral" rating. So, nothing too concerning here. Interestingly, this way of evaluating stocks is similar to the method Buffett himself uses.

Step 3:  Compare a stock's price-to-earnings ratio now to its P-E ratio in the past. This analysis can tell you if investors are more enthusiastic for a stock right now than they have been. It can be a warning sign. The Stock Selection Guide from BetterInvesting helps us do this analysis. Here, we find Berkshire Hathaway is in the "buy" range as long as it can maintain its historical earnings growth rate of 14.7%.

Step 4: Evaluate the company's financial strength. Getting a cheap price on the stock of a shaky company isn't a good deal if the company hits tough times. That's why it's good to understand how strong the company is. That's certainly not a problem with Berkshire Hathaway, one of just a handful of companies with the AAA credit rating from S&P. As a double-check, we can look up Berkshire's USA TODAY StockMeter score, which comes in at a neutral 2.7. See it here.

What's the bottom line? This analysis is somewhat mixed. But it's hard to make a case that Berkshire Hathaway shares are overly expensive, even at more than $100,000 each.

Just remember, no matter what the share price, you need to do your research based on the value, or market value, of the company.

Matt Krantz is a financial markets reporter at USA TODAY. He answers a different reader question every weekday in his Ask Matt column at money.usatoday.com. To submit a question, e-mail Matt at mkrantz@usatoday.com.