How to make a P-Chart without a computer?

K

KatheA

#1
Hi Everyone.
I need to control one of the processes where i work, it is mandated to be controlled by a live SPC, because the data is attribute and different sample sizes are present i need to do a P chart but there is not computer in the area for them to document the results. Is there an easy way to perform a P chart without a computer?

Thank you!
 
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Bev D

Heretical Statistician
Staff member
Super Moderator
#2
Re: P-Chart. How to perform one without a computer?

Use a calculator, pen and paper. it's how we did it in the 'old' days. (inteh ancient days we did the math in our head)

create a chart with the center line on it. put the formula for calculating the data point and it's associated control limits on the chart. Add spaces under each point plot 'column' to enter the sample size and number of defects and the calculated rate and limits. Train the operators how to do the math and plot the points and what the alarm rules are. Have a buddy check their work.

There is a somewhat easier approach if the sample sizes don't change much (I think it's less than 15%, I'd have to look it up) then you could plot the control limits ahead of time usign an average sample size. This way the operator only calculates the rate and plots the point...
 

Stijloor

Staff member
Super Moderator
#3
Re: P-Chart. How to perform one without a computer?

Use a calculator, pen and paper. it's how we did it in the 'old' days. (in the ancient days we did the math in our head)

create a chart with the center line on it. put the formula for calculating the data point and it's associated control limits on the chart. Add spaces under each point plot 'column' to enter the sample size and number of defects and the calculated rate and limits. Train the operators how to do the math and plot the points and what the alarm rules are. Have a buddy check their work.

There is a somewhat easier approach if the sample sizes don't change much (I think it's less than 15%, I'd have to look it up) then you could plot the control limits ahead of time usign an average sample size. This way the operator only calculates the rate and plots the point...
Bev,

If the sample sizes do not vary more than 25%, you do not have to recalculate the control limits. Source? "The Transformation of American Industry" training materials. (Taught this great program for many years...) ;)

Stijloor.
 
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