Dear reader,
For my science fair project, I plan to do the title... which plant can obsorb the meost odor in the bathroom. For the project I need a device to help me measure how much stinky odor is still left. Do u know where I could buy it? Thanks for your help!
Denise

I don't know that such a device exists for measuring the amount of odor that was there and still exists in a room. You might want to consult a dentist about this, because I know that they might have a meter that measures the amount of odor that someone might have in their breath. Something that they have might help you with your experiment.

Best of everything to you that you are trying to accomplish!

Yes, as clough says, odour detection is quite difficult and fairly expensive. You can buy sensors that will detect certain gasses, so maybe a methane or ammonia detector is what you would be looking for.
Most of these are designed for industry, rather than the kind of situation that you are in.
Also, most of the detectors will alarm when the gas goes over a certain limit, rather than giving you a read out of the concentration.

Having a quick look by googling "home methane detector", all the ones I can find will just trigger at 25% the explosive limit. This isn't too useful to you.

I'll keep thinking for a better way to do it. One big problem is that the smells in a bathroom naturally exit the room through windows and under doors and the like. Most of the dissipation of an odour will be due to this, rather than your plant.

You could try keeping a plant in a large airtight (glass) container. Introduce some smelly air. I'm not sure how you would measure the result though, except with your nose. But when you open the lid you would let normal air mix with the smelly air. Maybe you could have an airtight container with a pipe coming out the lid with a valve on top. Then you could smell the air by shaking the container (or swirling it or whatever), then opening the valve and smelling it. This would work well and not much fresh air would get in. With the airtight container, you run the risk of the plant starving of lack of CO2. You will also want another airtight container with no plant and the same smelly air, so you can compare the smells. You probably want to do the experiment several times to ensure the first time wasn't a fluke, and change the order that you smell the jars in so that you don't introduce error.

Hmmm..

I can't really think of a satisfactory way to do it without expensive equipment.
Do you have a local university or industry where you could ask for help, especially if they have a mass spectrometer? I'm sure plenty of people would like to help such a polite young lady, and could help you with the experimental procedure too. The mass spectrometer will give you an idea of exactly what compounds are in your gas in which proportions.

Apology if this is rambling a little. I wrote this while going through the thought process :)