Vertical plane repeatability?

I was wondering....
What is the best method to get repeatability in the vertical plane when working with a jig on a knee mill?
I now have a DRO, and lining up X,Y to a pre-determined center point on a jigs seems basic, but getting the knee/quill back in position?
Now, My DRO has the quill, but I can see factors such as the endmill being installed a hair higher/lower throwing that off. So you zero it, sure, but what is the reference? Do you just let the (stopped) endmill come down on top of the work and "sit" there to zero?
And what about the knee? Do you just count turns of the wheel and use a measuring tape to get it back to position? I realize there is a indicator holder on the side of the head, but the knee could be 13 inches away or the indicator seated slightly differently, even if it could reach the table. I know the knee probably doesn't matter so much as long as you can get the tool to zero in relation to it. The words "Height Guage" keep ringing in my head, but I thought I'd ask for the tricks and shortcuts from those who know best....

Thanks Again!
Sean S

Sean, the word you're looking for is pick-up or touch off. Most people have a short paralled or hunk of key stock the place on top of the work, bump the tool or end mill on it and set their quill stop or what ever.

If our looking for absolute three axis dinensional referencing, there aint no such animal on a turret mill. Every time you change the tool you have to establish the vertical reference. If you have a sophisticated 3 axis DRO with tool offsets and a guick change spindle tooling kit, you can pick up the reference once and go from tool to tool without fiddling.

You'll learn the tricks. They're all simple. If machine work was hard they'd have to pay machinists more money and I sure haven't seen anythin but scale plus premium.