Subject: how to measure the amount of stain left in carpet?Where to find device?

My 6th grade science project concerns testing 3 stain removers to see 
which one works best on stained carpet.  My teacher accepted the topic but 
now she says that it is not a good one because the conclusion cannot be 
scientifically reached.  She says that I cannot have a number of people 
just look at the carpet samples to decide which cleaners work best.  My 
grandma and I looked on the iinternet and found that there is something 
called a colorimeter.  Where could I find one that I might be able to 
use.  I don't have much money.  I have called laboratories from the 
yellowpages and school science departments.  Can I use something else?  Or 
where else should I Look?  Thank you, Emily

Re: how to measure the amount of stain left in carpet?Where to find device?