<p>(Set of 2) The Tropf-Blumat Maxi acts as a regulator and dripper, just like the standard Tropf-Blumat. This one is 9 inches long though. You put it in the ground 6 - 7.5 inches so it senses the moisture at a deeper level. This is important when your plants get bigger because the regular Blumat sensor might turn the water off too soon. And this one might turn it off too soon if your plant still has surface roots. Some growers use both - especially if they are growing in coco or a hydroponic system.</p>