Ive written a very basic UDF function to calculate 2 probabilities given several potential variables, but I keep receiving this error message and I am entirely stumped as to what to do. This is my first time using UDF, if someone could give me some pointers, I would greatly appreciate it. I have posted what I have written below.

Function PD(a As Variant, x As Variant, z As Variant)
PD = [a(1.00-x)] + [z(1.00-a)]
End Function
Function PS(a As Variant, x As Variant, z As Variant)
PS = (a * x) + [(1.00-a)*(1.00-z)]
End Function

But when I move to an excel sheet, and insert the respective equation, including telling the function which cells it should extract the variables from for the specific problem...I receive the error message¨Value!¨

Help?