Yes, multiply to get trees/volume per acre. You look at the property- should it be managed in one big piece, or is it, for example, 2 sides of a mountain with greatly different productivity- then you might do 2 seperate cruises. You do enough plots to get your absolute error/coinfidence interval (part of the calculations you'll be learning) so that you are pretty darn certain you are within, say, 10% (say "I am 90% sure that I am with 10% of the value"). The more regular the timber (i.e. plantation pine) the fewer plots you will need to get this certainty. Look at the property boundary on the topo map and run transects up and down the slope (easier than walking sideslope all the time) at some regular spacing, say 3 chains between transects, 4 chains between plots along the transect- whatever it takes to get as many plots as you need. In natural timber with some irregularity, you can bet you'll need 30 plots, to get your "confidence interval" certainty minimal.
Its confusing inthe classroom. Ask a forester if you can scribe for them sometime when they go cruise, and look over their shoulder when they run the numbers, thats essentially how I had to learn so that it really made sense.
