The ITBM by Carl Swendlin is calculated by adding the McClellan Oscillator to its 10-period EMA and then applying a 20-period EMA to the result. Example:
DataSeries ITBM = EMA.Series( yourMCOSeries + EMA.Series( yourMCOSeries, 10, EMACalculation.Modern ), 20, EMACalculation.Modern )
Its absolute value indicates the degree of market's overbought/oversold state. Market is getting stronger when the index is rising or weaker when it's falling, and it's better when the ITBM is above the zero line.