Average Function

I am attempting to Average across four unbound cells. Some may have values or may not. I am using the following formula:

=(Nz([Dif1],0)+Nz([Dif2],0)+Nz([Dif3],0)+Nz([Dif4],0))/(IIf(IsNull([Dif1]),0,1)
+IIf(IsNull([Dif2]),0,1)+IIf(IsNull([Dif3]),0,1)+IIf(IsNull([Dif4]),0,1))



Where: Dif1 = 1
Dif2 = 1
Dif3 = 1
Dif4 = 0

The answer being generated is 6 when it should be 1.

Thanks Again

This is in regards to Access 2003. "Nz" is in regards to Null values and IIf is the same as in Excel but for Access.

Dif1, Dif2, Dif3 and Dif4 are the names of the unbound cells in an Access 2003 form.