This is the second doweling jig I've owned.  It centers on the wood (front to back) far better than my first jig, but is more difficult to use.  The viewing ports for aligning left to right are small and difficult to see through.  Although using the alignment marks is tedious, I can't complain because I've drilled about 100 holes so far and the pieces have lined up very well.  You will need a set of drill bit collars to go with this jig.