If you work in forestry, especially with the type of job you might get right out of undergraduate, at some point you're going to be doing some forest measurement or mensuration. This might be as part of a timber inventory, or this also can be referred to as timber cruising. And there's a lot of reasons you might do it. I... in some cases it might be just to take an inventory of a forest stand to get an idea about what the volume is, what the basal area is, what the condition of the stand is. It might also be something that's done before a thinning, or before a timber sale, to get a good inventory of the trees. Or if you're doing scientific research, or have ecologic... ecological objectives, it might also be important to have an idea about the standing timber. So things that we might be interested in: basal area is something that we're often interested in. So you remember when we measure trees, we measure them at breast height. Basal area is a measure of the cross-sectional surface area of the tree, so if you were to imagine cutting down that tree at breast height and measuring the surface area of that stump, that would be the basal area of that tree. So... but we don't want usually just the basal area of an individual tree, we want the basal area of a stand, and typically we report that in square meters per hectare. So square meters of basal area per hectare. So that's one thing that we're interested in, and along with these other all sorts of measurements, we often want to have these measured by species, so knowing the total basal area of a stand is really important, but also knowing what proportion of that basal area is douglas fir, versus western hemlock, versus western redcedar, or western white pine... that's important as well. So basal area is something that's really important. And another key factor that we want to measure, or another key statistic that we want to measure, is volume. There are a number of ways to calculate the volume of a tree relatively precisely. For our purposes though, we're going to use more of an estimate approach. If you take that tree trunk and you imagine that it's a cone, then we can take the basal area of that tree, so the cross-sectional area of that tree trunk, multiply that by the height of the tree, and then divide by one-third, and that will give us a volume for that tree, or a volume estimate for that tree, in cubic meters. As I mentioned, basal area is something we can calculate for an individual tree, or we can scale it up to a stand level and give a measurement per hectare for the stand. We can do the same thing for volume. We can estimate the volume of an individual tree, or we can scale that up to the hectare and get the volume of wood per hectare for the whole stand, and we often will also split that up by species, because for management purposes, or timber purposes, knowing how many cubic meters per hectare of douglas fir versus western redcedar versus other species you have is very important.