Non-empty used with division in a calculated member

Hello,

Can you help with this.

I have 10,000 customers and 500 customers have values for measure A and B. If you use either of these measures you only see the 500 customers. I have a calculated measure C that is a division and to get round division by zero errors it's in an iif statement. It works fine but shows all 10,000 customers. Is there a way to make calculation C only show the 500 customers? 

Thanks very much, Brian

Brian Searle