Interpretation & Calculations
The V mask parameters are calculated as:
where Δ is the size of the shift in the process mean that the user desires to detect (i.e. the Amount of Concern,), and k is a scaling factor relating the vertical scale unit to the horizontal scale unit.
Lead Distance (d):
where N is the total number of observations (= n * m), and σx is calculated is the sample sigma .
Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).