Sigma Level Sigma Capability

Let me explain all the terms in sequence to understand better
What is sigma?

Its a measure of smaller the better
A measure that is used to quantify amount of variation in the process
What is sigma level?

Its a measure of Larger the better
A metric used to measure the performance of the process
Sigma Level = No of sigma between LSL & Mean, No of sigma between USL & Mean
Z = (USL-Xbar)/sigma; Z = (Xbar-LSL)/sigma
Minimum value of above two is taken.
It also called Z score
Relation between sigma level and Sigma Capability is

Capability = Z score/3