It definitely shows that this is one of the cheapest meters on the market. But the values seem to be realistic, when having all windows open it shows 450-460 pp

It definitely shows that this is one of the cheapest meters on the market. But the values seem to be realistic, when having all windows open it shows 450-460 ppm which is at least close to the global 400ppm ( and I live next to a road in a bigger city ).