Dax Calculate without filter parameter

Hi all,

I created a calculate table hoping to make calculations based on buyer emails.

I got what I want using Calculate function with putting any filter parameter.

I check the result again by creating measure and they are all correct.

But what confusing me is that how does it work?

How does dax know that the result should be filter by buyer email when Calculate is applied?

Data RelationUsing Calculate without filter got the correct resultWrong result without CalculateCompared with measure(left table) and Calculate Tabel(right table)

Thanks in advance.