GZAIR Indoor CO2 Meter, Data Logger, Wall Mountable & Tabletop Carbon Dioxide Detector, Air Quality Monitor, NDIR Sensor, Temperature and Relative Humidity, Time & Date, 0~9999ppm Range

The "instructions" are a sad, terse, one-pager with tiny print. The device always appears to be Locked, but You can unlock holding a button for a few seconds.You need to keep referring to the one pager and experiment. You have no prayer of understanding how it works but reading the documentation and experimenting.I bought 2 of these. One died after a year and a half. The other has lasted for 2 years so far.The device eats batteries. For some reason, plugging in the device will not allow it to work without installed batteries. And even when plugged in, the batteries drain. When they get too low, the device shows "LB", so you cannot read the CO2 level.

I have lost my manual and some other reviwer found the text to small.Can you post a pdf copy on your web page for Model 3 - or here

Has a logger included Stores over a month of data using a 10 minute log time. Download to excel Works great. We are using in a gym at our HOA to check ppm vs how many people in gym

In the picture, this unit is on the left. I took it and the two others outdoors for a test. Depending on where you are, outdoor CO2 levels should be from the high 300s to the high 400s ppm. The long running sensor on Mauna Loa, with just about zero interference from humans, animals, vehicles, and plant life, is at 420 ppm today. If you're around a lot of people and/or animals, or you're near traffic or other CO2 producing activity, even outdoors it could be well above 500 ppm.In my case this is on a back patio in the suburbs, with a very lightly traveled road about 120 yards behind my house, and a farm beyond that to the South. Prevailing winds are from the South to West. I've also got grass in my backyard and several decent sized trees, although I am in greater Phoenix in a desert region. Bottom line being that maybe with the right wind readings could be in the mid 300s ppm, but it's not likely.You can see the other two units are showing 387 and 408, and I've got more CO2 meters I've tried that read similar values around 400. No other unit has ever read below 350 ppm for this outdoor test, yet this unit is at an absurdly low 233. There is no way that is anywhere near correct. Since it's primary purpose is measuring CO2, that's got to be the lowest possible rating.As other reviewers have noted, this thing isn't easy to use either. I'm not sure I still have the manual, but most of these units have some degree of intuitiveness if you're technically savvy and you try the buttons for a bit. Note that it's plugged into a USB charger, so changing settings to reduce sampling time and thus save battery life is really irrelevant. Weak batteries are not a factor here, and I looked at the unit for a few minutes before taking the picture.The only setting I wanted to change anyway was the temperature units to Fahrenheit. On that reading this unit is a couple degrees above the other two when you do the conversion.Unfortunately, accuracy seems to be a question mark for most of these CO2 sensors. With digital thermometers of various types, I've been able to get very good correlation from unit to unit. Often with 1 degree or even less, since most of them have a tenths digit. Good luck getting that with any group of CO2 meters, as even a $300 model designed for lab use I saw elsewhere only lists +/- 30 ppm accuracy. The next model down was rated at +/- 50 ppm. So with the lower cost units here on Amazon, I'm not sure you can expect accuracy within +/- 100 ppm.This unit is well beyond even that.

Instruction booklet is microscopic if you are sight challenged you won't find a pdf manual online either. Still trying to set the date/clock and switch to Fahrenheit with no success.