Formual help

hello. I would like to create a formula on two variables, with a value condition on one of them.

my vars:

enc

compliance (values = I, R)

my report is a crosstab on compliance, so it looks like this;

I___R ____Sum Enc_Enc 10__10____30

i want to compute enounters (where compliance = R) / sum of encounters (for all encounters). So in my example, it would be 10/30, or 0.33

my current forumla looks like this like =<encounters>/Sum<encounters>

but i want to subset the numerator to encounters where compliance = 'R'. how do i do that? Thanks,

Andy