How do I plot a v-mask in excel?

JerryA

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Jul 10, 2008, 6:33:01 PM7/10/08

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Anyone know how to take a Cusum chart and plot a v-mask on it?

Andy Pope

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Jul 11, 2008, 3:38:35 AM7/11/08

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Hi,

And for those not in the know, what is a v-mask?

Cheers
Andy

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Andy Pope, Microsoft MVP - Excel
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Del Cotter

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Jul 11, 2008, 4:35:52 PM7/11/08

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On Fri, 11 Jul 2008, in microsoft.public.excel.charting,
Andy Pope <an...@andypope.info> said:
>And for those not in the know, what is a v-mask?

I googled, thinking "cusum" might be a typo for "custom", but it turns
out that "cusum" is a cumulative sum graph, a sort of alternative type
of control graph, and the V mask is the equivalent of the upper and
lower control lines. But, because this is a cumulative graph, instead of
being horizontal, they get closer together from left to right.

It wasn't clear to me, from the pictures I saw, whether the V lines are
straight or curved. If straight, this is just another case where a pair
of points, in a block of cells kept apart from the data columns, define
a line in an XY scatter graph. If curved, then they'll probably have to
be a series, and might as well be in spreadsheet columns alongside the
data.

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Del Cotter
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which goes to a spam folder-- please send your email to del3 instead.

JerryA

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Jul 11, 2008, 6:23:01 PM7/11/08

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Del is correct about the v-mask. Its useful for determining if a process
change is neccesary. And yes, the lines are straight, and actualy come to a
point off the chart. If any results of the cusum show outside the lines, then
something has occured. I just was wondering if anyone knows the formula to
make it work on excel.

Andy Pope

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Jul 12, 2008, 7:51:47 AM7/12/08

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Hi,

Well for the control chart there are explanations here,
http://processtrends.com/pg_charts_control_chart.htm
http://peltiertech.com/Excel/Charts/RunChtLines.html

As for a particular formula to calculate the v-mask lines we would need
much more detail.

Cheers
Andy

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JerryA

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Jul 14, 2008, 10:55:04 AM7/14/08

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Andy,
I already have done all the necessary calculations, and even have my Cusum
chart working perfectly, I also use the UCL and LCL charts, and a few others.
But I was just wondering if anyone knew how to use excel to automatically
draw the v-mask. The calculations are relatively easy, here is a website that
indicates how to manually draw a vmask, but I can't seem to translate it into
excel.
http://www.itl.nist.gov/div898/handbook/pmc/section3/pmc323.htm

Andy Pope

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Jul 14, 2008, 2:18:25 PM7/14/08

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Hi,

You would draw the lines using x,y coordinate pairs.
So if you have managed to create formula to calculate the
start/finish/corners of the line all you need to do is plot that as a
series.

Cheers
Andy

Bob

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Jul 31, 2008, 4:18:07 PM7/31/08

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use JMP, they have Cusum Chart module built in. Either one-sided or two-sided
charts.