Product review (5 stars): Instant measurements
The reason to choose this meter over many of the others is because it uses a laser/LED every 2 seconds to measure the CO2 levels, so the reading changes instantly.  Open a window and you can see the CO2 drop.  Breathe in its general direction and the CO2 goes up again.  Many of the other detectors use a chemical sensor that takes a lot longer to respond (if it doesn't have a digital readout don't buy).

It's really amazing to see how high the CO2 levels can get after even just minutes of exercise.  I set the central air blower to "on" now to keep CO2 in check, instead of "auto" to only run during heating/cooling.  Of course leaving a window is open is healthiest.

The instructions *are* poorly translated, but you only need to set it up once if you want Fahrenheit or to set the time.  Tab to the display you want to change, press other buttons to set.  Not too hard to figure out.