Interpretation & Calculations
The upper & lower control limits for the EWMA chart, when using the wandering mean formulation:
Ïƒp is the Prediction Error Sigma and
zt is the EWMA Forecast
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).