According to the statute, these three methods of determining alcohol concentration are identical (and that is the last we will speak about urine). If the concentration measured by blood and by breath are the same, that means for every 1 part of blood in your body you have 2100 parts of breath. This is also known as the partition ratio.
The problem is, no one runs a test to determine what the partition ratio is for the citizen accused of driving while intoxicated. There is, in fact, no scientific evidence to support the 2100:1 assumption. Estimates of actual partition ratios vary from 1100:1 to 3400:1! If a person's actual partition ratio is higher than 2100:1, the Intoxi-liar will overestimate his breath alcohol concentration.
This lack of a scientific standard could also lead to a very troubling result -- it is possible for a person to have an alcohol concentration of under .08 by one method of testing but have an alcohol concentration of over .08 by the other method! All the more reason you should NEVER submit a breath sample if you've been arrested for DWI.
Burping, belching or regurgitating prior to blowing in the Intoxi-liar may also produce a false reading due to the presence of mouth alcohol in the sample. The "slope detector" in the machine is supposed to prevent mouth alcohol from producing an inaccurate result -- but if the slope detector program is so reliable, why are breath test operators instructed to keep the test subject in their "continual presence" for 15 minutes prior to the test? Other sources of mouth alcohol are pockets around the base of the teeth due to gum disease and bits of food stuck between teeth or in dental work.
If you've been arrested for DWI, whatever you do, DON'T BLOW IT!