> test any other value Try this: Hyperventilate for a minute or two. Then, make a full exhale and hold it. You should be able to hold your breath for longer t

> test any other value Try this: Hyperventilate for a minute or two. Then, make a full exhale and hold it. You should be able to hold your breath for longer than you normally can and during this time you should see the value drop a bit. Be sure to inhale before you start getting dizzy or faint. (Note: do not do this under water)