formula 10% above and below average

Hi jonnyA 

I think you want to highlight the percentage in green (<total -10%) and highlight the percentage in yellow(>total+10%) in your Matrix.

You can try Conditional formatting feature in your Matrix.

I build a sample to have a test. In my Sample, total average is 20.93%. So show "%RT Count of CPT_Code" >30.93% in yellow and "%RT Count of CPT_Code" <10.93% in green.

Find conditional formatting in Format in Martix. You can use Background color or Font color.

Here I use Background color.

Result is as below.

For more details about Conditional formatting: Conditional formatting

Best Regards,

Rico Zhou

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