Rather that explain the problem. Its probably better to see it below. Having problems using the percentage difference column to compare a value between two tables.
In summary, I only want 3 columns in the below and not to show column 2.
And also if there is a null value, can it return zero so the percentage across works?
Code here - (ZN(SUM([Number of Records])) - LOOKUP(ZN(SUM([Number of Records])), -1)) / ABS(LOOKUP(ZN(SUM([Number of Records])), -1))
q1: it's hard to say without seeing pills you have in header but I assume that you pulled too much try removing unnecessary columns from the view or at least right click > uncheck show header
q2: try wrapping whole calculation with zn()
would be awesome to see .twbx file so we can give you better advice