SPC/Statistics > Statistics

The Statistics window gives the operator a current reading of relevant numerical information.
The following items will be found in the Statistics window:

  • Subgroup number (k).
  • Subgroup size (n).
  • ObsCnt = Observation Count = number of individual observations made.
  • XDBar = = X -double bar = the mean of the subgroup averages.
  • Rbar = average of the subgroup ranges.
  • s (all) = s
    s = = current standard deviation of inspection run
  • RBar/d2 = estimated standard deviation
  • Min = minimum observation value
  • Max = maximum observation value
  • Mean +/- 3,4,6s = control limits for XBar chart
  • Defect Ratio = percentage of measurements outside of tolerance
  • PPM = parts per million outside of tolerance
  • Cp = potential process capability index = (UTL-LTL)/6s
    where s = stnd.dev = RBar/d2
     
    more ...
  • Cpk = potential process performance index = Zmin/3 where Zmin = min {(UTL - )/s, ( - LTL)/s}, where s = RBar/d2
    more ...
  • CR = capability ration =1/Cp
  • CPL = ( - LTL)/3s, where s = RBar/d2
  • CPU = (UTL - )/3s, where s = RBar/d2
  • Pp = actual process capability index = (UTL-LTL)/6s where
  • Ppk = actual process performance index = Zmin/3 where Zmin = min {(UTL - )/s, ( - LTL)/s}, where

Statistics Chart