CF1:

=AND(NOT(ISBLANK($A1)),NOT(ISBLANK($B1)),$A1=$B1). ...amber

CF2:

=$B1$A1*1.1 .... red

CF3:

=OR($B1$B1,$B1<$B1) ... green

You may want to add the ISBLANK tests to CF2 and CF3

HTH

" wrote:

I know about the basics of boolean conditional formatting, ie. x<y,
xy etc. However, I want to be able to say that for example:

If xy colour yellow, but if xy by more than 10% then colour red, so
that I can see which of my results requires priority. Is there a way
to do this using conditional formatting?

I am using all three conditions as well, I have a traffic light system
in effect, if xy colour green, if x=y colour amber, if x<y colour
green.

thanks.