Sean, to me this is the crux of our building problem, what do we know, how do we know it and will it work the first time? Before specializing on tf, I worked on old buildings. Just about every building had foundation flaws and level reference became crucial concern. So I acquired a builders transit Vernier to 5 minutes and as I became more concerned about level and angular resolution I bought used a surveying transit, Lietz-Sokkisha with a direct read vernier to 20 seconds and a Brunson dumpy level with the level vial at 10 seconds per division. Having those instruments changed the way I thought about marking, measuring and building control. I was lead by the tools to incised layout and desire to match the frame to the existing field conditions, as close as I could measure. My basic method is square rule with numerical scribe mapping, as needed. If desired, I'll go into the process.