Ignoring cells with "-" when applying conditional formatting?

I have a table in which each cell contains a forumla to compare one number with another and return the % difference. If there's no data to compare against or an error the formula returns "-". I've applied conditional formatting so that any % increases over 6% or any decreases below 5% are highlighted, but it's also highlighting the cells with "-" in them.

Any ideas how I can get the cond. formatting to ignore these and leave them unshaded? I've tried adding another condition but it doesn't recognise the "-".

Thanks

Dear Jfarlow,

Pls try with the formula below in conditional formating
=ISNUMBER(A2)=FALSE

It is working, when I put that condition in 1st level.

cheers,
YKnet