discrimination of the measurement system?

As Jim explained, this has to do with MSA and not control charts.  It is probably a good idea to do an MSA before collecting data and plotting on a control chart.  If your measurement system has poor discrimination then the signals that might come from a control chart will have you needlessly chasing variation that can’t even be measured by your measurement system.  If your measurement system can only discriminate whole integers, reacting to points which might vary by the second decimal point, is just noise.  A nice conceptual analogy I like to use is time….one measurement system with really poor discrimination can only measure daytime and nighttime.  One slightly better might be able to discriminate by hour and an even better one down to minutes.  If you want to be able to identify time by seconds, none of the above measurement systems have sufficient discrimination.  If you want to be able to determine morning, afternoon and evening, one of the above will be sufficient.

You can perofrm this in Minitab or JMP and see the number of distinct categories (ndc). The idela is that it should be >4.

Yep, typo.  I hate it when I do that!

OOPS!  I meant the TO line, not the subject line.

You can use a technique called an ISOPLOT which is a special type of regression analysis (Scatter Diagram).  This is a technique developed by the late Dorian Shainin and is an excellent tool.
The Discrimination is figured by determining the Product Variation and dividing it by the Measurement Variation.  One must acheive 6 or greater.  10 is best.

Heay maaaan,
that ISOPLOT… It’s really groovy maaaaan.
maaaan, I’ve got the munchies
peace.

The Isoplot works fine for me and our processes despite your ignorant comments.
and your solution is?  I noticed you criticize often but have no solutions.  Please entertain us with your answer to the discrimination issue.

Bob,
There are two errors in my original post.  I said:
You perform the MSA, and you divide the sigma (parts) by the sigma (gage) and multiply by 1.14, then truncate the answer to an integer.
That sentence should have said:
You perform the MSA, and you divide the sigma (parts) by the sigma (measurement) and multiply by 1.41, then truncate the answer to an integer.
I do not know where the 1.41 comes from, but now that you asked, I am going to have to do a little study to see if I can find out.  It seems like we are picking up a sqrt(2) from somewhere.
Regards,
Jim Shelor

Bob,
The link below will take you to the derivation of the NDC equation.
http://www.minitab.com/support/docs/Answers/Root2.pdf
It shows where the 1.41 comes from.
I hope this helps.
Jim Shelor

Thanks much, your response was very helpful.  bob

Excellent  Elaboration