1. What is defference between Sigma & Z value.

2. When I shall calculate Sigma & when Z

Regds

Abhai

Sigma denotes the standard deviation. Shows extent of variation in a data set. Does not depend on mean or specification limit.

Z value denotes the sigma level for the process. It is a measure of process capability and depends on three elements for continuous data - the standard deviation, the mean and the specification limit. 

Dear Vishwadeep Sir ,

I read your response to the question . Feel much intrigued to ask . Suppose we have process currently running on 4.86 sigma , what does this means . Is it Sigma Level (z)  or Sigma - The Standard Deviation  ?

I am in complete harmony with what you said about z which depends on three factors - SD , SL , and Mean but much confounded with difference between Sigma and z .

 

 

Hi Rahul,

I hope this question has been answered by now. However, I thought I would put a post up to finish this off.

It sounds to me like it means z value.

z (upper)= (upper specification limit - the mean) / the standard deviation = 4.86

Regards

Clint

Agree with Steele,

Also, z (lower) = (the mean - lower specification limit) / the standard deviation

In cases where both the specification limits are known, the two z values need to be combined