I will admit to taking a few lazy ways out.
First of all, it is rare for me to have more than a few bends in a single piece of pipe. I'd just as soon put one bend or offset in a pair of short pieces, as try to get them just right on the first try.
Second, when I have to do a saddle, I will usually make the right saddle in a piece of pipe, then cut the pipe to place the saddle in the right place.
Third, box offsets can be a little large- just roll the pipe a little to the side. Or, better yet- get the $$$ Greenlee tool; then you can add the offset after you've bent the 90, or whatever. You can even add the offset on the wall.
Finally, you must have both an accurate right angle for reference, and a straight edge. Most of the time these are provided by either my truck, or a block wall.
I do almost all my pipe runs 'by eye,' rahter than using all the math. I don't think I've ever used the 'shrinkage' table! This works when you've got pipe runs off by themselves- if you've got a cluster of pipes, and it neds to look really good, then there's no getting away from a lot of layout and calculation. And re-work.
