Several years ago, I bought a medieval style box loom at Estrella War, a local event for the historical recreation group that I was active in at the time. I've since moved on to other activities, and the loom has been sitting unused. Poor little thing! But I found someone who is still active in the historical community, and I'll be passing the loom on to her this week. In preparation for that, I warped up the loom one more time, and took pictures of the process so she could see how I did it. That should give her a starting point for her own explorations.
So... Usually I use a warping board or mill to measure out my warp, but I'm pretty sure she doesn't have one of those. So I fell back on the old school method of setting up wood clamps to give me three uprights. I put two down at one end of the table to make my figure 8 cross around, and one down at the other end to measure out the length.