The key is to wrap every field or value in an Nz () function, not the entire expression. For instance, the following expression has the potential to return #Error, despite the Nz () function: ...

Why can I not set field property to Standard and get 2 decimals on values from a Nz function? Also, if I add a value from a Nz function and another value from a Nz function, the second will be added ...

Don't let Null values derail your formulas. See how to use the NZ function to convert the values to zeroes.