GB Cost calculator always calculates “Difference” on your arc level and is misleading. It would be better to show the “difference” based on the Arc level of the donation you selected. “80” “85” “90” “90.7” etc.
If I am putting in thousands of FP’s from1.90 thread, I dont need to know the difference of 90.7, I need to know the difference from what I have in there and the 1.90 I have selected.