So...I would like to highlight any cell in column 1 which is more than 2% different than the cell in the same row of column 2. This indicates a measurement error.
When you are trying to do this, don't compare it to the whole column, but look at cell level.
Let me start by giving a example to see if we are on the same page.
If H1 is 1 and Q1 is 1.02 then it is OK.
If H1 is 1 and Q1 is 0.98 then it is OK.
If H1 is 1 and Q1 is 1.03 or bigger then format change of H1.
If H1 is 1 and Q1 is 0.98 or smaller then format change of H1.
If this is OK use the following:
Select H1 and goto conditonal format.
Select formula is:
Now drag H1 down and select from the small square "format only".