Take Screenshot activity Clipping region parameters

Hi all, I’m trying to figure out the meaning of Clipping region parameters - Left, Top, Right, Bottom. I’ve searched similar topics, and did tests with at least 50 combinations. But those numbers do not make any sense to me. Where is the starting point? Plus, from time to time I’m getting an error “Save image: Object reference not set to an instance of an object”. As far as I understand, this error is because the clipping region is negative. So this is more “general sort of question”.
I’ve done a simple table in Excel with numbers from 1.1 to 9.9 and I want to take a screenshot of part of the table, my selector is number 5.5.
Thank you!