New Delhi, Aug. 26 -- Ask anyone who traded in January 2008. They will tell you the same thing. Everybody knew the market only went up. The Sensex had crossed 21,000. Your neighbour had a demat account, your barber had a tip, and nobody wanted to hear a warning.

Then, ten months later, it had lost more than half its value. Those who bought at the top spent years just getting back to even.

There was a number, back then, that had quietly gone to an extreme. Hardly anyone in India could see it at the time. Today, that same number is easy to check, and on the world's largest market, it's climbing again. That is worth ten minutes of your evening. Not to sell anything. To know what you are holding.

Start with the question every investor is r...