Be sure to keep the windows closed for 24 hours before starting the test. Put it in lowest livable area in the home, This would include a unfinished basement. Not a crawl space. Do not place it near any laundry, or heating equipment. Place it around 3 feet or table height. Leave exposed for three days. Note time and date when its set and when its closed back up again. Be sure to tape the can closed using the same tape if you can that comes with the kit. Also note weather conditions.
Remember this test is a screening test only. If results come back higher then 4, Get a professional company in to perform the test again using proper protocol to be sure that the first results are correct.