Density This is the easiest, and perhaps the most important thing that a succesful team needs to understand. As mentioned in the Sig pamphlet, balsa varies greatly, with Sig mentioning that it ranges from 4 to 24 pounds per cubic foot. When I first started building, I weighed the pieces by the stick. When I started Division IV, I started weighing them after I had cut them to 9 inch lengths, trying to reduce the variability. Even as balsa varies from piece to piece, one can also find variation within the piece.
Equipment can be a factor here.
Digital balances that go out to the hundredth's are nice, but one can get by with a 3 arm balance as long as you have some patience. The data in the Sig pamphlet shows an interesting trend if one compares the strength of the wood to it's weight. By looking at table 1, one can see that as the weight goes up, so do the various strengths. If one takes a look at the ratios comparing the strengths to the weight, one notices that the ratios are lowest for the low density wood, and highest for the high density wood. These values are shown in table 2.