Once you get this in hand you'll realize various temps in your house...around windows attics lighting...etc Would have paid $200 for this...and still would have gotten a great deal. if you chart the areas that are hot then you can target insulation installs. The area inside where my hot water heater was registered 102 because of attic exposure. Sealed it up and now its 76. Some ressesed lights leaked 88 degree heat...and I have 30 of them...In the attic I am exploring options on insulating specifically the worse ones. Doors where the key hole is leaks 90 degree heat...the vents were a solid 62 with air on...If you spray foam the roof line and rafters heat cant penetrate so your attic is like 80 instead of 120...your duckwork will be 80 and that's really good for summertime. Your AC will easily send cool air quickly because the its not fighting the temp of the attic. If you set your thermastat to 72 then you dont want 75 degree air leaking in...you want 72 degree air leaking in. This tool makes you an expert at finding heat and cool air leaks.