How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits)

K

KCIPOH

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 :confused:
 

Attachments

  • UCL and LCL_a.xls
    14 KB · Views: 423

bobdoering

Stop X-bar/R Madness!!
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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?
 
D

Darius

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.
 

Attachments

  • Average and Range Control Chart.ppt
    192.5 KB · Views: 548

bobdoering

Stop X-bar/R Madness!!
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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.
 
I

iamtroll

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. :agree1:
 
I

iamtroll

Thanks, that was a very nice and concise answer for the basics of how to create a control chart.:thanx:
 

bobdoering

Stop X-bar/R Madness!!
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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.

But the risk is starting at the wrong place, wasting time, frustrating operators and turning off everyone to the process. That, unfortunately, is the problem with a boss that is not willing to invest resources effectively and having an unrealistic expectation of the success of such a ill-thought out implementation. Cleaning up that mess - if it ever is cleaned up - will cost far more.
 
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