User Function Questions

[ChemistB]

I was playing with an Excel tip I received recently involving Summing every fourth cell in a row. One of the solutions was a User defined function that I think I copied correctly but it doesn't seem to work. Sometimes I get #Name? (thus it's not recognizing the function) and at other times it's giving me #value? (so my function isn't working properly). The file is attached.

Here are my User Function questions....
1. Does it go in a module, or under workbook or under the specific worksheet that it is being used in (or any of these)?

2. Can it be saved in my Personal Workbook and thus be used across workbooks?

Thanks in advance with any help on this.

ChemistB