Thanks, Sandra. I had only been through the cotton one, not the wool one. I had to watch both for it to "click."
I've made a sett chart of my own that will include columns for yardage per 100 grams to help me get used to the numbering system.
I've also gone through my Ravelry account and tagged all the yarns that seem obvious for weaving, like the Harrisville wool I have, and Henry's Attic, and lace weight singles which would work for weft better than warp.
Jane has completely changed the way I understand wrapping around a ruler, why negative space matters in weaving, why balance matters, and how to calculate the warp and weft for a project.
I do need to buy some cotton, for warp and for towels.