Two. What other interpretation coud you get from "NONE"?
Some swithces have a cneter OFF, some have center ON, and others have no ceter position. If your database of descriptioons (which could be a three-column table) needs an entry in each field, what else do you put?
Maybe it's just the way Engineers think, but it makes perfect sense to me... I understood exactly what was described, even before I looked at the catalog to see the other listings for comparison.