Understood! Thank you @Dawid 

yes! what I am using https://lookerstudio.google.com/reporting/. I cannot find out the ‘Table Calculation’ as the guide. I can only do as I explained above (and in the screenshot)Where I put my custom metric: Under the Metrics areas, click + Add Metr...

Hi, Thanks again for your very quick response. I do not know why my Looker is not the same look as yours. Here is mine. There is no Expression, just Formula. Doesn’t it the issue as I created my custom metrics on the wrong workplace?

@Dawid I faced the same issue. What I did exactly is shown in this guide :https://cloud.google.com/looker/docs/best-practices/how-to-calculate-percent-change-percent-previous ${ Internal Promotion Views} /offset(${ Internal Promotion Views}, -1) - 1 ...