Why does your data in column C start with a higher % than column A, but end with a lower percent than column A? If they were the same value, or a constant ratio you would get a straight line. Edit, should say a constant difference, not ratio, since the % is already a ratio.

Why does your data in column C start with a higher % than column A, but end with a lower percent than column A? If they were the same value, or a constant ratio you would get a straight line.