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October 1997

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Subject:
Re: fab, cleanrooms rating
From:
John Nelson <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Thu, 9 Oct 1997 11:54:13 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (19 lines) 
If you were to monitor your clean room with a calibrated instrument (Met One) and take multiple measurements each day of the number of 0.5 micron particles per cubic fot of air.  And then you
constructed an X-bar  control chart with a calculated mean and with control limits at +/- three standard deviations.  

What number would you use to state the class of your room?  Would you use the
mean number of particles per cubic foot or would you use the upper control limit 
as the worst case particle count?

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