VBA Excel MID Function Array

Question

In order to calculate a UPC Check Digit, I'm attempting to construct a function. I'll need to add the characters in places 1, 3, 5, 7, 9, and 11 and multiply by three as part of this. As a result, I presume that I want to utilise the MID function in my code, but I'm not sure how to use it to retrieve every other character since the MID method only allows me to choose one start digit. For example, I might write "CD = Mid(UPC, 1, 1)" in a line, but I need the first "one" in that formula to be (1,3,5,7,9,11). Do I have to concatenate my Mid function after writing it six times for each number? Or is it possible to obtain all those figures at once?