"The decision to remove low days, or intervals, means that a series of low days that results in a collective change will be ignored. If you have decided that removing those days makes sense, then measure the daily or intraday against a threshold created using the average minus one or two standard deviations of the .
Using a 1 standard deviation filter will remove the lowest 16% of the days; a 2 standard deviation filter removes 32% of the days. This type of filter is best applied to a index, such as On-Balance . For example, we find that the average on the New Stock Exchange is 1.5 billion shares, and 1 standard deviation of the is 0.25 billion shares. We decide that the filter is 2 standard deviations; therefore, any day with below 1.0 billion shares will be ignored." - Trading Systems and Methods, 2013.
This has a signal line which is subtracted from the filtered OBV to produce a simple oscillator giving signals above or below the 0 line.