格雷厄姆在他聪明的投资着一书里多次提到道琼斯工业指数（DJIA），在1959年，DJIA是584，有些长期的分析师就发表说明，这个已经太高，高到存在风险，那今天，我写作日2018年4月30日，DJIA是 24311.19。
由此我很好奇DJIA是怎样的一个指数，它是如何来衡量股市整体趋势，他从设立开始又发生了什么？带着这些问题，用着google , bing. wiki, baidu来了一遍自问自答。
1）定义：DJIA是一个股票指数，是由30家大型在美国上市的公司的总股价与道氏分母计算而得到
2017年10月1日更新的30家公司：
这30家现在总股价是：3530.81 usd, Dow divisor = 0.145234； DJIA = 3530.81 / 0.145234 = 24311.19
Company Price
MMM 3M196.12
AXP American Express99.61
AAPL Apple162.32
BA Boeing340.88
CAT Caterpillar144.72
CVX Chevron126.62
CSCO Cisco44.71
KO Coca-Cola43.31
DIS Disney99.23
DWDP DowDuPont Inc64.32
XOM Exxon Mobil77.79
GE General Electric14.38
GS Goldman Sachs239.8
HD Home Depot186.46
IBM IBM146.48
INTC Intel52.73
JNJ Johnson & Johnson128.27
JPM JPMorgan Chase109.4
MCD McDonald's158.3
MRK Merck59.47
MSFT Microsoft95.82
NKE Nike69.56
PFE Pfizer37
PG Procter & Gamble72.81
TRV Travelers Companies Inc133.19
UTX United Technologies122.46
UNH UnitedHealth240.18
VZ Verizon51.57
V Visa126.01
WMT Wal-Mart87.29
总计 3530.81
2）现在问题来了，dow divisor(道氏分母）怎么得来？
wiki说是道氏分母会根据股票分拆，结构变化等来调整 “The divisor is adjusted in case of stock splits, spinoffs or similar structural changes, to ensure that such events do not in themselves alter the numerical value of the DJIA. ”
2017年9月1日更新的道氏分母是0.14523396877348
“The Dow Divisor was 0.14523396877348 on September 1, 2017.[46] Presently, every $1 change in price in a particular stock within the average equates to a 6.885 (or 1 ÷ 0.14523396877348) point movement.”
so, that all , 这是我现在在网上可以查到的资料，其实我想知道他是怎么得出来，如果你有答案可以跟我分享。
3）看着DJIA是一路飙升，有种错觉，有周期，但股票市场definitely赚钱，easy to make money。但细看下，其实刚开始时DJIA是由12个公司组成一个指数，现在还在的就一个GE通用，其他公司已不在这30个公司列表里。
历史：DJIA组成的公司变过51次，以下是具体的变化的细节。这个让我想起格雷厄姆那句话，股市长期是个称重机，但前提是你得找到那个胖子。在关注这个胖子的成长过程中，如果他有开始减配变瘦的迹象，或是支撑企业成长的那个故事，市场变化时，也应该做出相应的对策。
The components of the DJIA have changed 51 times since its beginning in May 26, 1896. General Electric has had the longest continuous presence on the index, beginning in 1907. More recent changes to the index include the following:
On April 8, 2004, American International Group Incorporated, Pfizer Incorporated, and Verizon Communications Incorporated replaced AT&T Corporation, Eastman Kodak Company, and International Paper Company.[7]
On February 19, 2008, Chevron and Bank of America replaced Altria Group and Honeywell. Chevron was previously a Dow component from July 18, 1930, to November 1, 1999. During Chevron's absence, its split-adjusted price per share went from $44 to $85, while the price of petroleum rose from $24 to $100.
On September 22, 2008, Kraft Foods Inc replaced the American International Group (AIG) in the index.[8]
On June 8, 2009, General Motors Corporation and Citigroup were replaced by The Travelers Companies and Cisco Systems, the latter of which became the third company traded on the NASDAQ to be part of the Dow.[9]
On September 24, 2012, UnitedHealth Group replaced Kraft Foods Inc following Kraft's split into Mondelēz International and Kraft Foods Group.
On September 20, 2013, Goldman Sachs, Nike, and Visa replaced Alcoa, Bank of America, and Hewlett-Packard. Visa replaced Hewlett-Packard because of the split into HP Inc. and Hewlett Packard Enterprise[10][11]
On March 19, 2015, Apple replaced AT&T, which had been a component of the DJIA since November 1916.[12] Apple became the fourth company traded on the NASDAQ to be part of the Dow.
On September 1, 2017, DowDuPont replaced DuPont. DowDuPont was formed by the merger of Dow Chemical Company with DuPont.