Dataquest ART Tau Calculation

The formula for Tau is where M is the slope of a linear fit of the natural log (ln) of pressure points from min dP/dt to a terminus.  The terminus shall be set to 66% of the total pressure drop in the cycle.  We may choose to include the point or not based upon a confidence value from the linear fit.  Multiply the result by 1000 to change the units from seconds to milliseconds.