The options regarding air in your lungs: There really is an advantage in trying to expel all the air you can, because once you can achieve that level, it is pretty reliably constant. In our scale of things, within two or three letters is realistic, which commonly means within around 1%. In contrast, if you just try to "always have the same amount of air in your lungs, whether at a standard exhale or some average amount of air, our letters scale can show you why that is not very accurate! If you do it at what you consider a standard exhale, you will be at about 45 letters above (heavier) than the maximum expelling mode. The point being, one time it might be 40 letters and the next time it might be 50 letters, and your normal exhales might seem the same to you. If your data can be off either way by five or ten letters each time, the idea of trying to chart the results becomes less valuable! Your data might be varying by several percent just because of these differences. The value of expelling all the air you can is that once you get practiced at doing that, you are likely to have a rather consistent amount of air remaining in your lungs (very likely around 1.2 liters). Since that amount is pretty constant, your baton choices are more consistent and your results more accurate.
The precision of our Baton/Float system is clear with these facts. For an adult man, a single letter difference is often only around 1/4 of 1%! It is not possible for anyone to consistently exhale all their air to that precision, but coming within a few letters is reasonably done, which means a Bodyfat Percentage value within around 1% or so, and that is very repeatably true. You are certainly free to TRY to exhale exactly the same normal amount but you will quickly see that you will sometimes rise and sometimes sink! These comments also make clear why we need to consider the far smaller amount of intestinal gas present, as it can affect the results by several letters. The carbon dioxide released by a can of carbonated pop in your stomach might require as much as six or eight letters higher Baton!
Bodyfat Analysis (specifically directed at Childhood Obesity)
The storyline of the 30-second and one-minute PSA (Public Service Announcement) TV presentations.
The page that provides the PVC construction details for the Batons
and Floats and all the printable Analysis Charts is at:
http://mb-soft.com/public2/bodyfwp2.html
This is the page that has the Bodyfat Calculator which uses the Baton/Float letters and the dry body weight
( http://mb-soft.com/public/index.html )
C Johnson, Physicist, Physics Degree from Univ of Chicago