[Lynne]

Originally Posted by Battle_Ring

I entered

<if condition="$post[field13] = $post[field10]-$post[field11]"></if>

And nothing else shows up in psotbit at all

<if condition="$diff = $post[field10]-$post[field11]">
The difference is $diff.</if>

Does that work?

If you need it to be saved somewhere, then you will have to write a plugin to save it to the database. If you just need it spit out in the postbit, then just try what I wrote above.