Look at the total number of drinks you have had and compare that to the time shown. You can quickly tell if you are at risk of being arrested. If your BAC level is in the grey zone, your chances of having a collision are 5 times higher than if you had no drinks, and 25 times higher if your BAC level falls into the black zone. These charts are intended to be guides and are not legal evidence of the actual blood alcohol concentration. Although it is possible for anyone to exceed the designated limits, the charts have been constructed so that fewer than 5 persons in 100 will exceed these limits when drinking the stated amounts on an empty stomach.
Actual values can vary by body type, sex, health status, and other factors.
Also you can be unsafe with fewer drinks if you are tired, sick, upset, or have taken medicines or drugs.