Well hello there Mr.Kept_Wheat, one who knows-it-all.
It's best to use $x as your main variable. This variable is your stepping stone you might say. It dictates how many times to duplicate. Set this variable to
1 to
20.
Then use the $a as your unit number having an interval of 1. Skip whatever numbers with the skipper.
Open the manual manually inside the data>manual>index.html. Harhar.
See?! This thing solves everything. I wouldn't have referred it to you if it didn't work wonders.

EDIT: I used $a twice. Har har. Changed it. Read it!