[users] Calc - Format Error when Denominator = 0

[John Gilchrist]

Dear OOo Users,

In Calc:
    Score is defined as a cell, C1
    Events is defined as a cell, C2

I calculate "Average Score per Event" =Score/Events

This works well until Events = 0.
Then, this expression blows up.
   Err:503  

When the denominator, or Events,  =0, I want "Average Score per Event" to be 
either blank or zero.
Please, how do I do this???

Thank you,
John Gilchrist
Tulsa, OK