As I was sewing yesterday, I recall one of my favorite fashion design teachers saying " count your stitches when you make that turn at the bottom of the zipper". WHAT?
Well, after you sew to the bottom of your zipper (the bottom part of the U) and you make that horizontal turn which is only about 1/2 inch , you count your stitches until you hit the seamline and then as you cross it you count out the same number of stitches before you make your turn upwards.
I use 1/4 inch tape in each side of the seam line as a sewing guide but I still alway count my stitches to make sure it has been aligned correctly.
This technique assures that you will have a balanced zipper insertion.
Thank you MR. MARICH - I miss you but you still live in my ear!
I'm sure this is not very clear and wish I had the time to draw a picture but think of your zipper seam as a "U". The bottom of the U is where you start to count...hope that helps