The Hang Seng Index (HSI) is a benchmark for blue-chip stocks traded on the Hong Kong stock exchange. It was first published on November 24, 1969 and has been updated daily since then. The HSI is composed of the top 50 companies in Hong Kong, ranked by market capitalization.Some people see the HSI as a barometer of the overall health of the Hong Kong economy. When it goes up, they view this as a sign that things are good; when it goes down, they see it as a sign that things are bad. However, I believe that you can't rely on the HSI to give you an accurate picture of what's going on in Hong Kong - it's just too volatile. For example, back in September 2015, when China's stock market crashed, the HSI plunged along with it.Despite its volatility, I still think that tracking the Hang Seng Index can be useful for investors looking to invest in blue-chip stocks traded on the Hong Kong stock exchange.