Oh, when I saw 'centered double' I automatically thought 'decrease' because I don't think the term is used in increases.
There is a double increase though, the knit, yo, knit into one stitch which is pretty well centered. You can also knit front back front in one st, I don't know if that looks centered or not.
Dory, is it an increase or decrease you want? The pattern should explain somewhere how to do it.