Co2 meter to test if my co2 is low

Been looking at these and I already have one that reads above 400 and there is a tolerance that would allow 200 to read as 400 or 390 as 420. It’s the inkbird. Completely useless for my purposes

I need a decent 0-2000plus meter.

I’m trying to make sure my plants are using all co2 in a room. Thx.