I use API Windfloaters, basically they are the white dandelion fibers, and will even show how thermals are working. When you let them go, if the temp is warming they will actually rise with thermals, and if it is cooling the thermals are dropping they will fall as they float, and you can see exactly what your scent is doing. I also have used baking soda in a small plastic bottle with a "puffer" top. The bottle is an empty Tinks Gel bottle, you can open the lid, and give it a little squeeze and it will puff out a little white cloud to show direction.