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Actual rather than standardized spec values in capability boxplots

kennedy3

Community Trekker

Joined:

Jul 2, 2015

This is probably a simple one, but for some reason I can't find the answer on my own.  When I generate a capability boxplot, the x-axis is always a standardized spec.  That's useful to have when I have different specifications but I want to compare performance, but much of the time I have the same specification for an entire analysis.  When I present the results, my audience is often confused since my control limits are always -.5 to .5 rather than the measurements they're used to seeing.  Is there some way to turn off the standardized numbers?

 

5 REPLIES
Peter_Bartell

Joined:

Jun 5, 2014

I'm a little confused by the phrase "...my audience is often confused since my control limits are always -.5 to .5 rather than the measurements they're used to seeing." Since control limits don't usually come into the conversation when presenting process capability analysis results. One way you can come close to getting spec limits on a box plot is in the Distribution Platform's Capability Analysis submenu. If you add the spec limits and keep the histogram visible in the window, with the box plot shown above the histogram, the spec limits, while they don't extend all the way into the geography of the box plot, they are plotted at the appropriate positions for the x axis of the histogram which also extends up to the box plot.

kennedy3

Community Trekker

Joined:

Jul 2, 2015

The control limits are important because I'm showing the boxplots and not
the histograms. For this particular application, the boxplots are more
helpful and they'd be even more helpful if the x-axis was in the original
units.
Peter_Bartell

Joined:

Jun 5, 2014

You can also deselect the histogram, retaining the box plot, and add x axis reference lines.

tonya_mauldin0

Joined:

Jan 21, 2015

Peter is correct.  There is no way to do this in the Process Capability platform.  You can produce what you want using the Distribution platform.  You can turn off the histogram as Peter says and the box plots will be shown in the original data units with the spec limits also plotted in the original units.

kennedy3

Community Trekker

Joined:

Jul 2, 2015

I worked around this using a regular boxplot with some reference lines.  In other words, I arrived pretty much at the place you recommended.   Thanks!