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