So you're looking at the display and instantly you know what the value was last year, and how the seasonal variability affect whatever you see on the display?

So you're looking at the display and instantly you know what the value was last year, and how the seasonal variability affect whatever you see on the display? Whatever you're reading on your co2 sensor, thermometer, or any other sensor device RIGHT NOW is only indication of what's happening right now, in your location. That's not a global trend, not even a local trend. And having the sensor installed in incorrect place can mean that the data is worth less.