


28th December 2011, 09:42 PM


How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Hello Cove members,
I need help and would like someone to guide me on how to calculate UCL and LCL for the following attachment.
Can show me in detail for calculating the Mean, Std Dev (step by step)
Need help

29th December 2011, 04:41 AM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
A Quick Bump!
Can someone help?
Thank you very much!
Stijloor.

29th December 2011, 08:35 AM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
By looking at this data, I would have to ask what is this process? What kind of variable are you looking at? To calculate UCL and LCL, you have to pick the correct control chart. I see subgroups, but am not sure if they are adequate. What do the subgroups represent? Do you really want to calculate standard deviation long hand? Do you have a calculator or Excel?

29th December 2011, 09:38 AM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Sorry for deleting the previous response, I attached a file for powerpoint 2007 and saw that the file posted was on a previous version, so it can be seen, change it to 2003.

Thank You to Darius for your informative Post and/or Attachment!


29th December 2011, 09:45 AM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Quote:
In Reply to Parent Post by Darius
I attached a file for powerpoint 2007 ...

Great post. I still bothers me to dump data into a chart without understanding if the chart  or the data  is adequate. It is just a bad way to look at SPC. Borders rubber stamp. That's why I posed the questions before posting the chart.

Thanks to bobdoering for your informative Post and/or Attachment!


29th December 2011, 11:50 AM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Darius...how do you obtain A2 & D4 from the tables?

29th December 2011, 12:05 PM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Quote:
In Reply to Parent Post by AnaMariaVR2
Darius...how do you obtain A2 & D4 from the tables?

It depends on the sample size "n", see slide 4

Thanks to iamtroll for your informative Post and/or Attachment!


29th December 2011, 12:12 PM


Re: How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)
Quote:
In Reply to Parent Post by bobdoering
Great post. I still bothers me to dump data into a chart without understanding if the chart  or the data  is adequate. It is just a bad way to look at SPC. Borders rubber stamp. That's why I posed the questions before posting the chart.

I agree, but you have to start somewhere. If you have been tasked with charting a process, you often need to get on with it since your boss is not always willing to wait for you to gain the necessary knowledge to be an expert. I would hope that then that individual would recognize that their needs goes beyond the mechanics and must extend to the level of understanding. That understanding is not going to be found in this forum, as statistics need some fairly extensive study and training however we can help folks by giving folks a taste of what the statistics can tell them.

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