A person watching the tide coming in, and who wishes to know the spot which marks the high tide, sets a stick in the sand at the points reached by the incoming waves until the stick reaches a position to where the waves do not come up to it, and finally recede enough to show that the tide has turned. This method holds good in watching and determining the flood tide of the stock market. The average of [stock prices] is the peg that marks the height of the waves. Like those of the sea, the price waves do not recede all at once from the top. The force which moves them checks the inflow gradually, and time elapses before it can be told with certainty whether the high tide has been seen or not.”

— Charles Dow, creator of the Dow Jones Industrial Average, on January 31, 1901, edition of The Wall Street Journal