How to calculate errors (standard, Absolute or Absolute Relative)

I'm having difficulty in calculating each of the standard, Absolute or Absolute Relative errors in one formula. For example, I can calculate the AVG error in one column. And I have 3 more separate columns each with the error calculated by the aforementioned deviations. But how do I calculate the Avg error and the Standard in one formula (the same for avg error and Absolute and so on) whereas I get the same results?

- First, I think I got by deviation calculations correct.
- Second, I need a sample formula for each in the adjacent columns; Standard looks weird to me. (I, J and K)...

Please see attached-

Thanks so much....