Before I changed tables/fence I would measure the distance to the front of the table from the far left and right side of the fence. If it was tight bump it back a hair and measure, make another cut until you get the distance right.I've been using a Bosch 1181 router table for a couple of years now. While mostly it's ok, I am a bit fustrated on setting the fence distance to the bit. There are 2 knobs on each side and a cheesy distance gauge. It's hard to get the distance dead on with out some trial and error.
Recently, I was somewhat foiled when cutting a sliding dove tail joint using a 14 degree 1/2" bit. The side where you cut down the middle is fine, it's the other side where you take 2 cuts on each side of the "pin" which is tough. You are supposed to cut a little bit off, on each side, until it fits. This is like 1/32 or even 1/64 for a cut. That's hard to get set with this type of fence. I am tapping just a wee bit, but it's hard to do on both sides and know how far you've moved it. I was wondering if there are suggestions for a better way to go at this.
I also would mark a pencil line on the table where the fence is and use that as a reference point.