These definitions begin with the basics (advance-decline statistics) and then work their way down to the formulas (McClellan Oscillator, McClellan Summation Index). These indicators are based on percentages, not absolute values. The Russell 2000 has 2000 stocks and the Nasdaq 100 has 100 stocks. Because the Russell 2000 has 1900 more stocks than the Nasdaq 100, we cannot really compare indicators that use absolute numbers like Net Advances (advances less declines). Instead, it is more robust to calculate advances, declines, net advances, advancing volume and declining volume as a percentage of the whole. This makes it possible to compare breadth indicators for the Russell 2000 against breadth indicators for the Nasdaq 100. This also makes it possible to compare breadth indicator across a whole range of indices and ETFs.
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Advance%

The number of advances as a percentage of advances plus declines. If there were 400 advances and 100 declines in the S&P 500, then Advance% would equal 80%. 400/(400+100) = 400/500 = .80 = 80%.
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Decline%

The number of declines as a percentage of advances plus declines. If there were 400 advances and 100 declines in the S&P 500, then Decline% would equal 20%. 100/(100+400) = 100/500 = .20 = 20%.
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AD Net%

Advance% minus Decline%. Using the examples above, AD Net% would equal +60% (80% - 20% = +60%). Readings above +50% show above average strength and readings below -50% show above average weakness. Big moves often start with a big advance (above 80%) or a big decline (below -80%) in AD Net%.
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AD Line

A cumulative measure of AD Net%. The AD Line is a running total of AD Net%. Positive AD Net% increases the cumulative value and the line moves higher. Negative AD Net% decreases the cumulative value and the line moves lower. The plot of AD Line can then be compared to the price plot of the underlying security to affirm or question the trend. A strong security should also have a strong AD Line. Weakness in the AD Line often foreshadows weakness in the security and visa versa.
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McClellan Oscillator

The McClellan Oscillator is a short-term momentum indicator for breadth that uses the difference between two exponential moving averages (just like MACD). Marian and Sherman McClellan developed the McClellan indicators and detailed information can be found at the McClellan website (Click Here). The formula is as follows:

19-period EMA of AD Net% - 39-period EMA of AD Net%

The McClellan Oscillator oscillates above and below the zero line. It is positive when the shorter (faster) moving average is greater than the longer (slower) moving average and negative when the shorter moving average (faster) is less than the longer moving average (slower). The indicator can be used just like MACD or any other momentum oscillator. Signals are derived from positive and negative divergences, crosses above and below the zero line or overbought and oversold readings.
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McClellan Change

The absolute change in the McClellan Oscillator from the previous close. If the oscillator moves from -20 to -10, then the change would equal +10. If the oscillator moves from +40 to +20, then the change would be -20.
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Alerts

An alert is triggered when the McClellan Oscillator moves above or below the zero line. BullX signals a bullish crossover or a move from negative territory to positive territory. BearX signals a bearish crossover or a move from positive territory to negative territory.
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McClellan Summation Index

The McClellan Summation Index is a long-term breadth indicator based on the McClellan Oscillator.
In a nutshell, the McClellan Summation Index is a cumulative measure of the McClellan Oscillator.
Each period's Oscillator reading is applied to the previous day's Summation Index. This makes the
Summation Index a running total of the Oscillator values. Positive Oscillator readings increase
the Summation Index and move it higher. Negative Oscillator readings decrease the Summation Index
and move it lower. The original formula is as follows:

1000 + Previous Day's McClellan Summation Index
+ Current Day's McClellan Oscillator.

Marian McClellan added 1000 to keep the index in positive territory. This also makes the indicator
oscillate above and below +1000.

Mathematician James Miekka developed a different formula for the Summation Index and Tom McClellan
has endorsed this formula. In the original formula, the value of the Summation Index depends on
when the calculation was started and one must know the previous value of the Summation Index. This
presents a chicken and egg problem. Miekka's formula solves this problem by not requiring the
previous value. The Miekka formula is as follows:

(19 x 39-period EMA of AD Net%) -
(9 x 19-period EMA of AD Net%)

Miekka originally added 1000 to jibe with the original formula. The version above does not include
the artificial addition of 1000 and therefore oscillates above the below the zero line. This makes
it easier to identify positive and negative crossovers. Strong trends develop when the indicator
remains positive or negative for a sustained period of time. The indicator can be used just like
any other momentum oscillator. Signals are derived from positive and negative divergences, crosses
above and below the zero line or overbought and oversold readings. On the short-term chart, a 20-
day EMA is overlaid and investors can look for crosses above and below this moving average for
signals as well. The long-term chart uses a 50-day EMA.
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