when index prices and the indicator are moving in different directions then the current index trend may lack strength bullish divergence occurs when the oscillator is rising while the index is falling this indicates the index could head higher soon since more stocks are starting to advance 
bearish divergence is when the index is rising and the indicator is falling this means fewer stocks are keeping the advance going and prices may start to head lower 3the difference between the mcclellan oscillator and mcclellan summation index the mcclellan oscillator was developed by sherman and marian mcclellan who also developed the mcclellan summation index 4 the mcclellan summation index adds the current day s mcclellan oscillator to the previous day s mcclellan summation index in other words the summation index is a cumulative measure whereas the oscillator is not while the oscillator may be more useful for analyzing shorter term trends the summation index is more applicable to broader and longer term price trends 3limitations of using the mcclellan oscillatorthe indicator tends to produce lots of signals breadth thrusts divergence and crossovers all occur with some frequency but not all these signals will result in the price index moving in the expected direction the indicator is prone to producing false signals and therefore should be used in conjunction with price action analysis and other technical indicators 2the indicator can also be quite choppy moving between positive and negative territory rapidly such action indicates a choppy market but this isn t evident until the indicator has made this whipsaw move a few times study how the indicator acts over extended periods of time and in different market conditions before relying on the indicator for trading purposes 