Conditional formatting of entire column

Hello,

I have two columns in excel 2010 which are generated by sensors measuring the same thing. In theory the 2 columns should be the same...of course they are not ;).

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.

I tried something like -> {cell value < ="($Q:$Q)" applies to =$H:$H }which works for direct comparison but if I change it to ="($Q:$Q)*0.98" or ="($Q:$Q)"*0.98 it doesn't work. Is there a way to do column math in this situation.

I know I could make another column and do the math there and then format that but I already have LOTS of columns so I would rather not. This is also only one of many other conditions imposed on the data so it is not just adding one extra column it would be many more.

I am trying to use conditional formatting as a filtering technique, the reason being that I need to filter in time not just values. Meaning I need a certain temporal stability in the reading before the datapoint is valid so if I simply begin filtering data then I may loose the temporal data from adjacent rows, I need 5 minutes worth and the data is taken at 30s intervals. I plan to conditionally format the entire dataset and then filter by format.

an alternate suggestion on how to filter this would be fine or if you know how to do math on column comparisons that would be great.

thanks