As I recall from my PC training in forestry and soil conservation work a tarea is a unit of measurement for one days work. A varra is 30 inches long. Therefore a tarea of firewood is the amount that a woodcutter should be able to cut , with an axe, in a reasonable work day. there is always regional variations on this. For example, I recall that a tarea of firewood could be either one varra by two varras or one varra by four varras. A big difference, which throws off the whole days work thing. Where it really gets screwed up is with land measurement. The standard measurement for land was the cuerda. In Chimaltenango a cuerda was, I recall, 40 varras square(1600 sq. varras), but in Quiche and elsewhere a cuerda was 30 varras square(900 sq. varras) or even 25 varras square(625 sq. varras. Theoretically, a cuerda is the amount of land that can be worked, by hand, in one day, i.e. a tarea. We use to know all this stuff, because we worked with it every day. Coincidentally, my pace(step) was one varra, so I could easily pace off distances and come up with a reasonable estimate in sq. varras or cuerdas. Also my arms just happened to be the magical varra in length, and I could quickly count off lengths of rope, etc. I guess I'm the optimum size man in Guatemala. Or at least at some point in it's past.