Sigma Level Shift is the difference between the within (also known as short term) performance and the overall (also known as long term) performance. Basis the process and data observations Motorola estimated that overall capability of the process is 1.5 less than the within capability (though this number may vary from process to process and industry to industry).
An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Himanshu Sharma on 22nd Nov 2022.
Applause for all the respondents - M V Ramana, Anuj Bhatnagar, Gulshan Kumar, Himanshu Sharma, Mohamed Safir, Rahul Arora.