Question

Calculate the control limits for a c chart with a process average equal to 4 nonconformities.

Answer 1

The 3-sigma control limits for c chart are given below:

UCL = c +3VC

CLc=c

LCL = -3Vc

where $\bar{c}$ average number of process nonconformities and we are given $\bar{c}=4$.

Therefore,

UCL = 4+3V4

  

= 4+3 x 2

  

=446

$=10$

CLc=c

$=4$

LCL = -3Vc

  $=4-3\sqrt{4}$

$=4-6$

$=-2=0$

We took LCLc as we can't have a negative number of nonconformities for controlling.